Title of Invention	REINFORCED FRICTION MATERIAL
Abstract	WE CLAIM: 1. A reinforced friction material having two distinct phases joined by a cured binder, and comprised of: a honeycomb core reinforcement having multiple, adjoining, open-ended cells separated by cell walls and constituting a three-dimensional continuous phase: mixed friction particles and filler particles contained within said reinforcement open-ended cells and constituting a three-dimensional discontinuous phase and cured organic polymer binder binding said mixed friction particles and filler particles and said reinforcement into a unitary part by covalent bonds and electrostatic bonding

Title of Invention

REINFORCED FRICTION MATERIAL

Abstract

WE CLAIM: 1. A reinforced friction material having two distinct phases joined by a cured binder, and comprised of: a honeycomb core reinforcement having multiple, adjoining, open-ended cells separated by cell walls and constituting a three-dimensional continuous phase: mixed friction particles and filler particles contained within said reinforcement open-ended cells and constituting a three-dimensional discontinuous phase and cured organic polymer binder binding said mixed friction particles and filler particles and said reinforcement into a unitary part by covalent bonds and electrostatic bonding

Full Text	Attorney Dookot Mo. ABX4 96 This invention relates generally to friction materials useful for incorporation in various brake assemblies and other friction-producing devices, and particularly concerns the fabrication of a reinforced friction material having an embedded honeycomb core for reinforcement. The use in automobiles and other transport vehicles of various braking devices such as drum brake assemblies, disc brake assemblies, and the like is well-known. Such devices function to retard or stop vehicle motion, often from high velocities and at high rates of vehicle deceleration. In the braking process much or very nearly all of the vehicle's kinetic energy is converted to frictional heat at the surfaces of the friction material or materials incorporated in the vehicle braking devices. Such braking process also frequently results in very high operating temperatures being developed in the friction material or materials. Friction materials incorporated in the known braking devices have generally utilized discrete reinforcement fibers or continuous reinforcement filaments for material reinforcement purposes, and often with a compromise as to one or more of the material's qualities of wear-resistance, developed braking noise, and release of fiber debris. U.S. Patent No. 3,639,197 issued in the name of Spain, for instance, discloses the use of both continuous carbon filaments and randomly-oriented short carbon fibers as reinforcements in the rotor and stator composites of an aircraft brake assembly. U.S. Patent No. 3,759,353 issued in the name of Marin teaches the use of both circumferentially-wound carbon filament and woven carbon filament cloth reinforcements in a disc brake friction disc composite structure. U.S. Patent No. 4,373,038 issued in the name of Moraw et al. teaches an asbestos-free friction material useful for brake linings, clutches, etc. and comprising a combination of discrete aramid fibers, mineral fibers, and steel fibers reinforcing a hardenable binder. U.S. Patent No. 4,384,640 issued in the name of Trainor et al. discloses a friction composite wherein aramid fibers only, sometimes in continuous filament form and sometimes in discrete fiber form, are utilized as reinforcements in the fabrication of various brake or clutch components. U.S. Patent No. 4,418,115 issued in the name of Le Lannou teaches a friction lining material for use in brakes, clutches, and other applications having both mineral tibers and organic fibers as reinforcements in a mixture having fillers and a binder. The organic fibers are at least partially composed of a crosslinkable fusible type such as acrylic or modacrylic fibers. U.S. Patent No. 4,997,067 granted in the name of Watts also teaches a friction material for brakes, clutches, etc. wherein the reinforcing medium is a woven fabric that includes fluorine (polytetrafluorethylene) fibers in yarn form. See also U.S. Patent No. 3,365,041 granted in the name of Stormfeltz for a friction clutch teaching of the earlier conventional use of both asbestos fibers and glass fibers in a woven reinforcing fabric that is embedded in a friction material composition having also fillers and phenol formaldehyde resin binder. As to teachings concerning noise reduction in a braking device, see U.S. Patent No. 5,083,643 issued in the name of Hummel et al. and assigned to the assignee of this invention. The friction material disclosed therein incorporated reinforcement fibers which are more particularly described as being glass fibers, rock wool fibers, processed mineral fibers, or refractory material fibers. This invention offers performance advantages over the friction materials referenced above, particularly with respect to resonance noise reduction, increased wear resistance, more consistent friction material performance, and minimizing release of fiber debris. Other advantages will become apparent from a careful consideration of the described invention and of the method of friction material fabrication or manufacture that is detailed and claimed. SUMMARY QF THE INVENTION SUMMARY OF THE INVENTION In order to achieve the objectives of this invention we provide a vehicle brake assembly or the like with one or more cooperating brake friction elements (e.g., a disc brake friction pad or a drum brake friction shoe) fabricated to include an improved reinforced friction material. The improved reinforced friction material, which is typically fiber-free or contains relatively small amounts of discontinuous fibers in order to obtain desired frictional and wear characteristics is appreciably carbonaceous in nature. It is comprised of a cured mixture of friction modifier particles, filler particles, a polymer resin binder, and an embedded reinforcing core. The reinforcing core eliminates the need for discrete reinforcement fibers or continuous reinforcement filaments within the friction material. Some of the mixture particles also may accomplish a special function such as lubrication. The friction material reinforcing core, which has multiple, adjoining, open-ended cells, is embedded in the particle or powdered mixture during brake element friction material fabrication in a manner whereby, following polymerization of the friction material polymer resin binder, the reinforcing core cells are filled completely with the cured mixture being bonded to the cell walls. Examples of the carbonaceous particles utilized include graphite particles, carbon black particles, coke particles, and rubber particles. Examples of useful filler particles include metal particles, metal oxide particles, and baryta a.nd other mineral particles. Examples of useful reinforcing core materials include expanded aluminum honeycomb core, welded steel honeycomb core, glass fiber-reinforced phenolic resin honeycomb core, and like expanded core materials. Examples of discontinuous fibers used to modify frictional or wear characteristics within the friction material mixture include steel wool, carbon, milled glass, mineral, fiberglass and Kevlar fibers. It is believed that the reinforced friction material of this invention also may have advantageous application to the manufacture of clutch mechanism friction components, and to use applications other than automotive. Throughout the drawings and description which follow, frequent illustration and reference will be made to reinforcing cores having adjoining, open-ended core cells with a hexagonal cell cross-sectional configuration as being reinforcing honeycomb cores. The term as used in this application is intended to include reinforcing cores with adjoining, open-ended cells of different cross-sectional configurations such as square, rectangular, triangular, trapezoidal, rhomboidal, and the like cross-sectional (planform) configurations. Accordingly the present invention provides a reinforced friction material having two distinct phases joined by a cured binder, and comprised of: a honeycomb core reinforcement having multiple, adjoining, open-ended cells separated by cell walls and constituting a three-dimensional continuous phase: mixed friction particles and filler particles contained within said reinforcement open-ended cells and constituting a three-dimensional discontinuous phase and cured organic polymer binder binding said mixed friction particles and filler particles and said reinforcement into a unitary part by covalent bonds and electrostatic bonding. The present invention also provides a method of manufacturing a reinforced fiiction material as hereinabove described, comprising the steps of placing and evenly distributing a first measured quantity of a friction material mixture comprised of friction particles, filler particles, and binder particles in a mold cavity having a planform corresponding to the planform of said fiiction material shape; placing a honeycomb core reinforcement in said mold cavity with complete penetration of only a lower portion of said reinforcement through said evenlv distributed friction material mixture. placing and evenly distributing a second measured quantity of said friction material mixture in said mold cavity to completely fill the upper portion of said honeycomb core reinforcement; and compressing said placed and evenly distributed friction material mixtures to an elevated isostatic pressure and elevating the temperature of said placed and evenly distributed friction material mixtures to form said reinforced friction material shape. With reference to the accompanying drawings, in which Figure 1 is a plan view of a disc brake friction pad assembly having a preferred embodiment of the improved friction material of this invention incorporated therein; Figure 2 is an elevational view taken along line 2-2 of Figure 1; Figure 3 is an enlarged view of a portion of Figure 2; Figures 4 through 7 are schematic sectional views of compression molding apparatus at successive stages of use in the manufacture of friction material structured utilizing the preferred honeycomb core depicted in Figures 1 through 3 in accordance with our invention; Figure 8 is a plan view of an alternate form of disc brake friction pad assembly also having the improved friction material of this invention incorporated therein; Figure 9 is a perspective view of a drum brake friction shoe assembly having the friction material of this invention incorporated therein; Figures 10 through 13 illustrate different cell cross-sectional geometries produced during the manufacture of known honeycomb core materials; Figure 14 is a sectional view taken along line 14-14 of Figure 8; Figure 15 is a sectional view illustrating an alternate embodiment of a honeycomb core; and Figures 16 through 18 are schematic sectional views of compression molding apparatus at successive stages of use in the manufacture of frictional material structured utilizing the honeycomb core reinforcement depicted in Figure 15. Figures 19 through 21 are schematic sectional views of compression molding apparatus at successive stages of use in the manufacture of frictional material structured utilizing the honeycomb core reinforcement depicted in Figure 8. Figures l and 2 illustrate, in plan and in elevation, respectively, an automobile disc brake friction pad assembly (10) comprised of a base plate component (12) and friction pad component (14) securely bonded to the base plate component by a suitable adhesive (16) such as an epoxy adhesive. Base plate component (12) typically is a steel stamping and also is typically provided with mounting holes (18) for use in incorporating the friction pad assembly (10) into an automobile wheel disc brake installation. Friction pad component (14) is fabricated of the improved friction material of this invention, and is essentially comprised of a heat-cured, friction particle, filler particle, and binder particle mixture with an embedded reinforcement core. Friction pad components (14) may contain some discontinuous discrete fibers where necessary to obtain desired frictional or wear characteristics. In the drawings the heat-cured friction material mixture is designated (20) and the embedded reinforcement core is designated (22) . Although this description refers to a heat-cured friction material, it should be noted that the binder utilized in the friction material may be non-heat curable. For example, some binders cure at ambient temperature. It should be noted from details in the drawings that reinforcement core (22) is in all cases constructed of multiple, adjoining, open-ended cells defined by cell walls. However, the cells may have different cross-sectional geometries depending upon the applicable method of honeycomb reinforcing core. manufacture. In many instances a hexagonal cell cross-section planform is preferred. (See Figures 1, and 8 through 10, for example). Other available core cell cross-sectional configurations are illustrated and described in connection with Figures 11 through 13. In general we presently prefer honeycomb reinforcement cores made of aluminum alloy, fiber-glass reinforced phenolic, aramid reinforced with phenolic or epoxy, fiber-glass reinforced polyimide, carbon fiber-reinforced polyimide, thermoplastics, thermosets, mineral, ceramics, metal or metal alloy, or combinations of the aforementioned materials or other comparable materials. Such cores normally have a bulk (expanded) density of approximately 2 pounds per cubic foot or greater. In some cases core density, as determined by applicable cell size, cell wall thickness, and cell wall material, may extend to as much as approximately 2 0 pounds per cubic foot for an expanded carbon fiber-reinforced polyimide material having 3/16 inch wall-to-wall, open-ended cells. It should be noted that we prefer honeycomb reinforcement cores in which the cell walls are spaced apart a distance ranging between about 1/16 inch and about 1 inch. If the walls define circular cells we prefer the cells to have a diameter ranging between about 1/l6 inch and about 1 inch. Also, generally the ratio of the weight of the expanded honeycomb reinforcement core to the total weight of the reinforced friction material is in the range of approximately 5% to 20%. Such compares favorably also to conventional fiber-reinforced friction materials and continuous filament-reinforced friction materials wherein the weight of the fibrous reinforcement alone generally exceeds 20% of the total weight of the friction material. A preferred method for embedding the selected reinforcement core (22) in the friction material mixture (20) is illustrated schematically in Figures 4 through 7 of the drawings. Of course this is not the only process for making a honeycomb reinforced friction pad. As shown in Figure 4, a lower mold half (30) having a cavity (32) and ejector pins (34) is preferably preheated to a temperature of approximately 320 degrees Fahrenheit and a conventional release agent is applied as a coating to cavity (32). Cavity (32) has a planform shape and size that conforms to the shape and size of the friction material component that is to be fabricated. Next, approximately forty.percent (40%) of the required powdered mixture (36) necessary to produce the fabricated part is placed in cavity (32) and distributed evenly. It should be noted that if the powdered mixture (36) contains some discontinuous fibers to obtain desired frictional or wear characteristics the fibers preferably should have a length of no more than about one fourth the distance between opposing cell walls or the diameter of circular cells. Figure 5 illustrates the next process step involving the placing of a pre-cut and expanded honeycomb reinforcement core (38) within mold cavity (32) and with honeycomb core (38) penetrating the distributed mixture (36) until contacting the lower surface of the mold cavity. Basically, the axes of the core cells are oriented at right angles to the lowermost surface of cavity (32). Afterwards the manufacturing process is continued by placing the remainder of the required powdered mixture (3 6) necessary to produce the fabricated part in mold cavity (32) and distributing it evenly over honeycomb reinforcement core form (38) to thus completely fill all of the core cells. See Figure 6. As shown in Figure 1, an upper mold half (40), also preferably pre-heated to approximately 320 degrees Fahrenheit, is next assembled to lower mold half (3 0) causing the lower surface of upper mold half punch feature (42) to contact the distributed full quantity of mixture (36) and cause it to become compressed. We prefer that the compression forces applied to mold halves (30 and 40) be sufficient to generate an isostatic compression pressure of approximately 600 pounds per square inch throughout mixture (3 6). Next the interior of filled cavity (32) is vented to the atmosphere at l-minute, 2-minute, and 3-minute elapsed times following initial compression. Thereafter, the compression forces are preferably increased to a level that will produce an isostatic compression pressure of approximately 1200 pounds per square inch in the compressed mixture and that level of compression is preferably maintained for a period of approximately 2 minutes. Lastly, the so-compressed and partially cured part is next ejected from the mold assembly using ejector pins (34) and is subsequently transferred to a curing oven. In the oven the part is heat cured by raising the friction material temperature linearly to approximately 300 degrees Fahrenheit over a 3 hour period and then maintaining the heated part at the 300 degree Fahrenheit temperature for an additional 4 hours of process time. After cooling to ambient temperature the fabricated friction material part is ready for finishing and subsequent incorporation into the braking device or the like component for which it is intended. An alternate honeycomb core reinforcement (24) may be seen by referring to Figure 15. Core (24) has adjoining, open ended cells defined by walls the same as core (22) depicted in Figures 1 through 9. Core (24) also has a facing sheet (26) attached to one end of its cell walls. Sheet (26) provides additional rigidity for reinforcement core (24). A method for embedding the alternate honeycomb reinforced core (24) depicted in Figure 15 in a friction material matrix is illustrated schematically in Figures 16 through 18. As shown in Figure 16, a lower mold half (43) having a cavity (44) and ejector pins (45) preferably is heated to a temperature of approximately 320 degrees Fahrenheit and a conventional release agent is applied as a coating to cavity (44). Cavity (44) has a planform shape and size that conforms to the size and shape of the friction material component that is to be fabricated. Thereafter, reinforcement core (24) is placed in cavity (44) with facing sheet (26) engaging the bottom of cavity (24). It may be seen that the axes of the core cells are oriented at right angles to the surface of facing sheet (26) and to the lowermost surface of cavity (44). Thereafter, the manufacturing process is continued by placing the required friction material mixture (46) necessary to produce the fabricated part in mold cavity (44) and distributing it evenly over honeycomb reinforcement core (24) to thus completely fill all of the core cells. See Figure 17. Turning to Figure 18, it may be seen that upper mold half (47) , also preferably preheated to approximately 320 degrees Fahrenheit, is next assembled to lower mold half (43) causing the lower surface of upper mold half punch feature (48) to contact the distributed full quantity of mixture (46) and cause it to become compressed. Preferably the compression forces applied to mold halves (43 and 47) are sufficient to generate an isostatic compression pressure of approximately 600 pounds per square inch throughout mixture (4 6) . Next the interior of filled cavity (44) is vented to the atmosphere at one minute, two minute and three minute elapsed times following initial compression. Thereafter, the compression forces are preferably increased to a level that will produce an isostatic compression pressure of approximately 1200 pounds per square inch in the compressed mixture and that level of compression is preferably maintained for a period of approximately two minutes. Lastly, the so-compressed and partially cured part is next ejected from the mold assembly using ejector pins (45). Subsequently the part is transferred to a curing oven tc be heat-cured by raising the friction material temperature linearly to approximately 300 degrees Fahrenheit over a three hour period and then maintaining the heated part at the 300 degree Fahrenheit temperature for an additional four (4) hours of process time. After cooling to ambient temperature the fabricated friction material part is ready for finishing and subsequent incorporation into a braking device or like component for which it is intended. In Table 1 below we provide details of three examples of friction material matrix compositions that have been utilized in the fabrication of our improved reinforced friction materials having an embedded honeycomb core reinforcement (22 and 24). The mixture designated "Mix 1" has, when cured, a friction level suitable for avoiding thermal fade when used with glass fiber-reinforced composite honeycomb cores having an expanded density greater than about 8 pounds per cubic foot. The mixture designated "Mix 2" is satisfactory for use with honeycomb cores fabricated of sheet or foil aluminum (e.g., 5052 wrought aluminum alloy) and having an expanded density of at least about 5 pounds per cubic foot. The mixture designated -"Mix 3" includes some discontinuous carbon fibers which are desirable where increased wear or fade resistance is required. This mixture is suitable for use with glass fiber reinforced composite honeycomb cores having an expanded density greater than about 8 pounds per cubic foot. It has been found that where discontinuous fibers are added to a powdered mixture in the manufacture of a friction material part the fiber length preferably should be less than about one fourth the distance between opposing wall cells or of the diameter of the cells if they are round to ensure good fill of the honeycomb core walls. If the preferred fiber length is utilized good fill of the core cells will occur regardless of the percentage of discrete discontinuous fibers added to the mixture. All constituent values are given on a percentage parts by weight basis. In dynamometer testing of various honeycomb core-reinforced friction materials it was observed that certain disc pad components incorporating honeycomb core reinforcements having an expanded density of less than about 5 pounds per cubic foot sometimes exhibited a tendency toward hairline cracking. To overcome the hairline cracking problem, we originated a hybrid disc brake pad in which the friction material with honeycomb core reinforcement is bounded at its planform edges and on one face by a different but compatible friction material. Figure 8 illustrates the resulting hybrid disc brake friction pad assembly (50) in which the friction pad component (52) bonded to steel base plate component (54) has an invwardly-situated principal friction material area (56) fabricated with an embedded low-density honeycomb core inserted within a cup or walled receptacle (58) of compatible friction material area. The friction material area (56) may or may not be centered within the pad component (52). Indeed, friction material area (56) may be laterally or longitudinally offset in pad component (52) and may occupy a relatively small portion of the total area of pad component (52). The compatible friction material may or may not have a high thermal conductivity. If a high thermal conductivity is desired, a semi-metallic material may be utilized for the receptacle. Fabrication of a hybrid disc brake friction pad assembly having a central friction material area (56) fabricated with an embedded honeycomb core and encased in a walled receptacle (58) may be accomplished utilizing the following described process. A first mold for fabrication of the central material area (56) is heated to a temperature of approximately 230 degrees Fahrenheit. Next, approximately forty percent (40%) of the required powdered mixture for the central friction material area (56) is placed in the lower mold cavity and distributed evenly. Thereafter, a pre-cut and expanded honeycomb reinforcement core is inserted into the lower mold cavity with the honeycomb core penetrating the distributed mixture until contacting the lower surface of the lower mold cavity. Subsequently, the remainder of the required powdered mixture necessary to produce the central area (56) is placed in the lower mold cavity and distributed over the honeycomb reinforcement core form to completely fill the core cells. Thereafter the mold upper half is assembled to the lower mold half causing the lower surface of the upper mold half punch to contact the full quantity of mixture and cause it to be compressed. A compression force of approximately 200 pounds per square inch is applied for approximately three minutes to make the preform. This process is identical to that described previously in Figures 4 through 7. Thereafter, the so-made central friction material area (56) is removed from the first mold. Subsequently, the central friction material area (56) is placed in a second mold assembly (72) having a planform of the final pad as may be seen by referring to Figures 19 through 21. This mold (72) is preheated to a temperature of 320 degrees Fahrenheit. The area (56) is inserted into the central portion of lower mold half (74) of the second mold and the mixture (55) comprising the walled receptacle (58) is distributed evenly along the perimeter (57) of the area (56) and across the top surface (59) of the area (56). Subsequently, the mold upper half (76) is assembled to the mold lower half (74) to cause a compression force to be applied to the central area (56) and the mixture (55) forming the walled receptacle (58). Preferably a compression force of approximately 1200 pounds per square inch is applied to a second mold for a minimum period of two minutes. Thereafter the so compressed and partially cured part is ejected by pins (78) from the second mold assembly (72) and transferred to a curing oven where it is heat cured. An example of a satisfactory semi-metallic, non-reinforced friction material for a hybrid disc brake friction pad assembly is given in the Table 2 which follows as "Mix 4". Again,, all constituents are stated on a percentage parts by weight basis. Figure 9 illustrates the present invention as applied to a drum brake friction shoe assembly designated (60) . Assembly (60) includes an arcuate shoe table (62) joined to and supported by a perpendicular shoe web (64). A friction shoe component (66), having an arcuate under surface that corresponds to and mates with the upper surface of arcuate shoe table (62), is secured to the upper surface of shoe table (62), by an interface adhesive (68) . Other known fastening techniques, such as the use of rivets or the like, may be utilized to join friction shoe (66) to shoe table (62) in preference to use of an adhesive. In the brake shoe construction illustrated in Figure 9 it is important that friction shoe (66) be fabricated using. the reinforced friction material of our invention. The presence of the embedded honeycomb core reinforcement in the friction material matrix is clearly shown in Figure 9. Figures 10 through 13 are provided in the drawings to illustrate some of the different cell cross-sectional geometries that are obtainable in commercially available honeycomb core reinforcement materials. The illustrated honeycomb core fragments are designated 70, 80, 90, and 100, respectively. Generally, as stated above we prefer to use honevcomn cores with core cell sizes in the range from as little as approximately 1/16 inch (minimum distance measured from cell wall to opposite cell wall in the expanded condition) to as much as 1 inch. Also, as previously indicated, we basically prefer to define the incorporated or embedded honeycomb reinforcement core in terms of its bulk (expanded) density which typically ranges from as little as approximately 2 pounds per cubic foot to as much as approximately 20 pounds per cubic foot and which is influenced significantly by the core cell wall thicknesses, by the density of the particular material from which the core cells are configured, and by the core cell cross-sectional dimensions. The new reinforced friction material of this invention preferably does not contain fibers, either discontinuous or continuous, as a reinforcement. This is especially achievable in those instances wherein the honeycomb core reinforcement is made of a metal (e.g., aluminum). Even in cases wherein the honeycomb core reinforcement is made of a glass fiber-reinforced or carbon fiber-reinforced material such as a glass fiber-reinforced phenolic composite or a carbon fiber-reinforced polyimids composite the quantity of fibrous material in the fabricated friction material product is small in comparison to a conventional fiber-reinforced friction material. For instance, a honeycomb core reinforced friction material fabricated using Mix 2 of Table 1 above utilized an embedded honeycomb core reinforcement made of 27.6% glass fiber by weight and 72.4% of phenolic resin by weight. Because the reinforcement core comprised only 10.8% by weight of the completed friction material, the actual fibrous material content of the reinforced friction material was only 2.98% by weight. This level of fiber content is significantly lower than the typical 20% or more fiber content of known fiber-reinforced friction materials. The reinforced friction material made in accordance with the method of this invention is processed without the necessity of having to uniformly mix discontinuous fibers with powder (particulate) mixture constituents except where small amounts of such fibers are utilized to obtain desired frictional or wear characteristics, and thus avoids a major cause of manufacturing quality fluctuation. A substantially fiber-free mixing procedure is a much more efficient mixing process and results in a significantly improved consistency of quality. Also, in wear-resistance testing to date the new reinforced friction material has shown considerably lower wear rates of 0.07% compared to 0.35% for a fiber-reinforced friction material under the same test conditions. It is generally understood that the contact stiffness between the friction material and the rotor or drum affects the occurrence of brake noise. In order to eliminate or reduce the propensity of brake noise, it is often necessary to adjust the stiffness of friction material to an optimum value. However, for conventional friction materials, this essentially means reformulation of the materials and may result in other adverse consequences. The current invention successfully solves this problem by incorporating honeycomb cores into friction materials. Once a mixture has been formulated for a particular application, the stiffness of the pad can be changed by adjusting the stiffness of the reinforcement core to avoid brake noise. The frictional characteristics of the pad will remain almost unchanged because the cured mixture covers most of the contact surface area. Lastly, in conventional fiber-reinforced friction materials an uneven distribution of fibers often results in uneven brake rotor or brake drum wear treatment manifest by surface grooving. In comparison, Krauss and inertia dynamometer testing of the new reinforced friction material of our inventions was noted to result in very smooth brake rotor wear. Other suitable materials, component shapes, and component sizes may be utilized in the practice of this invention. Since certain changes may be made in the above-described system and apparatus not departing from the scope of the invention herein and above, it is intended that all matter contained in the description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. WE CLAIM: 1. A reinforced friction material having two distinct phases joined by a cured binder, and comprised of: a honeycomb core reinforcement having multiple, adjoining, open-ended cells separated by cell walls and constituting a three-dimensional continuous phase: mixed friction particles and filler particles contained within said reinforcement open-ended cells and constituting a three-dimensional discontinuous phase and cured organic polymer binder binding said mixed friction particles and filler particles and said reinforcement into a unitary part by covalent bonds and electrostatic bonding. 2. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of aluminum alloy. 3. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of glass fiber-reinforced cured phenolic resin. 4. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of glass fiber-reinforced cured polyimide resin. 5. The reinforced friction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of carbon fiber-reinforced polyimiede resin. 6. The reinforced friction material as claimed in claim I wherein said honeycomb core reinforcement is comprised of an iron alloy. 7. The reinforced friction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of an aramid material. 8. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of a thermoplastic material. 9. The reinforced friction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of a ceramic material. 10. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement open-ended cells each have a cell cross-sectional planform selected from the group comprised of triangular, square, rectangular, trapezoidal, rhomboidal and hexagonal cross-sectional planforms. 11. The reinforce friction material as claimed in claim 1 wherein said honeycomb core reinforcement has a bulk (expanded) density in the range of from approximately 2 pounds per cubic foot to approximately 20 pounds per cubic foot. 12. The reinforced friction material as claimed in claim 1 wherein said honeycomb core reinforcement has a facing sheet attached to one end of said cell walls. 13. The reinforced friction material as claimed in claim 1 wherein said mixture of friction particles and filler particles also includes discontinuous fibers. 14. The reinforced friction material as claimed in claim 13 wherein said discontinuous fibers have lengths less than about one-fourth the distance between the opposing cell walls of said honeycomb reinforcement core or the diameter of the cells if they are circular. 15. The reinforced friction material as claimed in claim I wherein said opposing cell walls of said honeycomb core reinforcement are spaced apart a distance from about one-fourth inch to about one inch. 16. The reinforced friction material as claimed in claim 1 wherein said cell walls of said honeycomb core reinforcement have a diameter ranging from between about one-sixteenth inch to about one inch. 17. The reinforced friction material as claimed in claim 1 further coraprisisng; a base element having structural rigidity;and securing means for securing said reinforced friction material to said base element. 18. The reinforced friction material as claimed in claim I wherein said honeycomb core reinforcement is non-metal. 19. A method of manufacturing a reinforced friction material claimed in any one of the preceding claims, comprising the steps of: placing and evenly distributing a first measured quantity of a friction material mixture comprised of friction particles, filler particles, and binder particles in a mold cavity having a planform corresponding to the planform of said friction material shape; Placing a honeycomb core reinforcement in said mold cavity with complete penetration of only a lower portion of said reinforcement through said evenly distributed fiiction material mixture. placing and evenly distributing a second measured quantity of said friction material mixture in said mold cavity to completely fill the upper portion of said honeycomb core reinforcement; and comprising said placed and evenly distributed fiiction material mixtures to an elevated isostatic pressure and elevating the temperature of said placed and evenly distributed fiiction material mixtures to form said reinforced fiiction material shape. 20. The method as clamed in claim 19 wherein said honeycomb core reinforcement placed in said mold cavity in penetrating relation to said friction material mixture has a bulk (expanded) density in the range of from approximately 2 pounds per cubic foot to approximately 20 pounds per cubic foot. 21. The method as claimed in claim 19 wherein opposing cell walls of said honeycomb core reinforcement are spaced part a distance of from about 1/16 inch to about 1 inch. 22. The method as claimed in claim 19 wherein said cell walls of said honeycomb core reinforcement have a diameter ranging from about 1/16 inch to about 1 inch. 23. A reinforced friction material, substantially, as hereinabove described and illustrated with reference to the accompanying drawings. 24. A method of manufacturing a reinforced friction material, as hereinabove described and illustrated with reference to the accompanying drawings.

Full Text

Attorney Dookot Mo. ABX4 96
This invention relates generally to friction materials useful for incorporation in various brake assemblies and other friction-producing devices, and particularly concerns the fabrication of a reinforced friction material having an embedded honeycomb core for reinforcement.

The use in automobiles and other transport vehicles of various braking devices such as drum brake assemblies, disc brake assemblies, and the like is well-known. Such devices function to retard or stop vehicle motion, often from high velocities and at high rates of vehicle deceleration. In the braking process much or very nearly all of the vehicle's kinetic energy is converted to frictional heat at the surfaces of the friction material or materials incorporated in the vehicle braking devices. Such braking process also frequently results in very high operating temperatures being developed in the friction material or materials.
Friction materials incorporated in the known braking devices have generally utilized discrete reinforcement fibers or continuous reinforcement filaments for material reinforcement purposes, and often with a compromise as to one or more of the

material's qualities of wear-resistance, developed braking noise, and release of fiber debris. U.S. Patent No. 3,639,197 issued in the name of Spain, for instance, discloses the use of both continuous carbon filaments and randomly-oriented short carbon fibers as reinforcements in the rotor and stator composites of an aircraft brake assembly.
U.S. Patent No. 3,759,353 issued in the name of Marin teaches the use of both circumferentially-wound carbon filament and woven carbon filament cloth reinforcements in a disc brake friction disc composite structure.
U.S. Patent No. 4,373,038 issued in the name of Moraw et al. teaches an asbestos-free friction material useful for brake linings, clutches, etc. and comprising a combination of discrete aramid fibers, mineral fibers, and steel fibers reinforcing a hardenable binder.
U.S. Patent No. 4,384,640 issued in the name of Trainor et al. discloses a friction composite wherein aramid fibers only, sometimes in continuous filament form and sometimes in discrete fiber form, are utilized as reinforcements in the fabrication of various brake or clutch components.
U.S. Patent No. 4,418,115 issued in the name of Le Lannou teaches a friction lining material for use in brakes, clutches, and other applications having both mineral tibers and organic fibers as reinforcements in a mixture having fillers and a binder. The organic fibers are at least partially composed of a crosslinkable fusible type such as acrylic or modacrylic fibers.
U.S. Patent No. 4,997,067 granted in the name of Watts also teaches a friction material for brakes, clutches, etc. wherein

the reinforcing medium is a woven fabric that includes fluorine (polytetrafluorethylene) fibers in yarn form. See also U.S. Patent No. 3,365,041 granted in the name of Stormfeltz for a friction clutch teaching of the earlier conventional use of both asbestos fibers and glass fibers in a woven reinforcing fabric that is embedded in a friction material composition having also fillers and phenol formaldehyde resin binder.
As to teachings concerning noise reduction in a braking device, see U.S. Patent No. 5,083,643 issued in the name of Hummel et al. and assigned to the assignee of this invention. The friction material disclosed therein incorporated reinforcement fibers which are more particularly described as being glass fibers, rock wool fibers, processed mineral fibers, or refractory material fibers.
This invention offers performance advantages over the friction materials referenced above, particularly with respect to resonance noise reduction, increased wear resistance, more consistent friction material performance, and minimizing release of fiber debris. Other advantages will become apparent from a careful consideration of the described invention and of the method of friction material fabrication or manufacture that is detailed and claimed.

SUMMARY QF THE INVENTION
SUMMARY OF THE INVENTION
In order to achieve the objectives of this invention we provide a vehicle brake assembly or the like with one or more cooperating brake friction elements (e.g., a disc brake friction pad or a drum brake friction shoe) fabricated to include an improved reinforced friction material. The improved reinforced friction material, which is typically fiber-free or contains relatively small amounts of discontinuous fibers in order to obtain desired frictional and wear characteristics is appreciably carbonaceous in nature. It is comprised of a cured mixture of friction modifier particles, filler particles, a polymer resin binder, and an embedded reinforcing core. The reinforcing core eliminates the need for discrete reinforcement fibers or continuous reinforcement filaments within the friction material. Some of the mixture particles also may accomplish a special function such as lubrication. The friction material reinforcing core, which has multiple, adjoining, open-ended cells, is embedded in the particle or powdered mixture during brake element friction material fabrication in a manner whereby, following polymerization of the friction material polymer resin binder, the reinforcing core cells are filled completely with the cured mixture being bonded to the cell walls. Examples of the carbonaceous particles utilized include graphite particles, carbon black particles, coke particles, and rubber particles. Examples of useful filler particles include metal particles, metal oxide particles, and baryta a.nd other mineral particles. Examples of useful reinforcing core materials include expanded

aluminum honeycomb core, welded steel honeycomb core, glass fiber-reinforced phenolic resin honeycomb core, and like expanded core materials. Examples of discontinuous fibers used to modify frictional or wear characteristics within the friction material mixture include steel wool, carbon, milled glass, mineral, fiberglass and Kevlar fibers.
It is believed that the reinforced friction material of this invention also may have advantageous application to the manufacture of clutch mechanism friction components, and to use applications other than automotive.
Throughout the drawings and description which follow, frequent illustration and reference will be made to reinforcing cores having adjoining, open-ended core cells with a hexagonal cell cross-sectional configuration as being reinforcing honeycomb cores. The term as used in this application is intended to include reinforcing cores with adjoining, open-ended cells of different cross-sectional configurations such as square, rectangular, triangular, trapezoidal, rhomboidal, and the like cross-sectional (planform) configurations.

Accordingly the present invention provides a reinforced friction material having two distinct phases joined by a cured binder, and comprised of:
a honeycomb core reinforcement having multiple, adjoining, open-ended cells separated by cell walls and constituting a three-dimensional continuous phase:
mixed friction particles and filler particles contained within said reinforcement open-ended cells and constituting a three-dimensional discontinuous phase and
cured organic polymer binder binding said mixed friction particles and filler particles and said reinforcement into a unitary part by covalent bonds and electrostatic bonding.
The present invention also provides a method of manufacturing a reinforced fiiction material as hereinabove described, comprising the steps of
placing and evenly distributing a first measured quantity of a friction material mixture comprised of friction particles, filler particles, and binder particles in a mold cavity having a planform corresponding to the planform of said fiiction material shape;
placing a honeycomb core reinforcement in said mold cavity with complete penetration of only a lower portion of said reinforcement through said evenlv distributed friction material mixture.

placing and evenly distributing a second measured quantity of said friction material mixture in said mold cavity to completely fill the upper portion of said honeycomb core reinforcement; and
compressing said placed and evenly distributed friction material mixtures to an elevated isostatic pressure and elevating the temperature of said placed and evenly distributed friction material mixtures to form said reinforced friction material shape.
With reference to the accompanying drawings, in which
Figure 1 is a plan view of a disc brake friction pad assembly having a preferred embodiment of the improved friction material of this invention incorporated therein;
Figure 2 is an elevational view taken along line 2-2 of Figure 1;

Figure 3 is an enlarged view of a portion of Figure 2; Figures 4 through 7 are schematic sectional views of compression molding apparatus at successive stages of use in the manufacture of friction material structured utilizing the preferred honeycomb core depicted in Figures 1 through 3 in accordance with our invention;
Figure 8 is a plan view of an alternate form of disc brake friction pad assembly also having the improved friction material of this invention incorporated therein;
Figure 9 is a perspective view of a drum brake friction shoe assembly having the friction material of this invention incorporated therein;
Figures 10 through 13 illustrate different cell cross-sectional geometries produced during the manufacture of known honeycomb core materials;
Figure 14 is a sectional view taken along line 14-14 of Figure 8;
Figure 15 is a sectional view illustrating an alternate embodiment of a honeycomb core; and
Figures 16 through 18 are schematic sectional views of compression molding apparatus at successive stages of use in the manufacture of frictional material structured utilizing the honeycomb core reinforcement depicted in Figure 15.
Figures 19 through 21 are schematic sectional views of compression molding apparatus at successive stages of use in the manufacture of frictional material structured utilizing the honeycomb core reinforcement depicted in Figure 8.

Figures l and 2 illustrate, in plan and in elevation, respectively, an automobile disc brake friction pad assembly (10) comprised of a base plate component (12) and friction pad component (14) securely bonded to the base plate component by a suitable adhesive (16) such as an epoxy adhesive. Base plate component (12) typically is a steel stamping and also is typically provided with mounting holes (18) for use in incorporating the friction pad assembly (10) into an automobile wheel disc brake installation. Friction pad component (14) is fabricated of the improved friction material of this invention, and is essentially comprised of a heat-cured, friction particle, filler particle, and binder particle mixture with an embedded reinforcement core. Friction pad components (14) may contain some discontinuous discrete fibers where necessary to obtain desired frictional or wear characteristics. In the drawings the heat-cured friction material mixture is designated (20) and the embedded reinforcement core is designated (22) . Although this description refers to a heat-cured friction material, it should be noted that the binder utilized in the friction material may be non-heat curable. For example, some binders cure at ambient temperature.
It should be noted from details in the drawings that reinforcement core (22) is in all cases constructed of multiple, adjoining, open-ended cells defined by cell walls. However, the cells may have different cross-sectional geometries depending

upon the applicable method of honeycomb reinforcing core. manufacture. In many instances a hexagonal cell cross-section planform is preferred. (See Figures 1, and 8 through 10, for example). Other available core cell cross-sectional configurations are illustrated and described in connection with Figures 11 through 13. In general we presently prefer honeycomb reinforcement cores made of aluminum alloy, fiber-glass reinforced phenolic, aramid reinforced with phenolic or epoxy, fiber-glass reinforced polyimide, carbon fiber-reinforced polyimide, thermoplastics, thermosets, mineral, ceramics, metal or metal alloy, or combinations of the aforementioned materials or other comparable materials. Such cores normally have a bulk (expanded) density of approximately 2 pounds per cubic foot or greater. In some cases core density, as determined by applicable cell size, cell wall thickness, and cell wall material, may extend to as much as approximately 2 0 pounds per cubic foot for an expanded carbon fiber-reinforced polyimide material having 3/16 inch wall-to-wall, open-ended cells. It should be noted that we prefer honeycomb reinforcement cores in which the cell walls are spaced apart a distance ranging between about 1/16 inch and about 1 inch. If the walls define circular cells we prefer the cells to have a diameter ranging between about 1/l6 inch and about 1 inch. Also, generally the ratio of the weight of the expanded honeycomb reinforcement core to the total weight of the reinforced friction material is in the range of approximately 5% to 20%. Such compares favorably also to conventional fiber-reinforced friction materials and continuous filament-reinforced friction materials wherein the weight of the fibrous

reinforcement alone generally exceeds 20% of the total weight of the friction material.
A preferred method for embedding the selected reinforcement core (22) in the friction material mixture (20) is illustrated schematically in Figures 4 through 7 of the drawings. Of course this is not the only process for making a honeycomb reinforced friction pad. As shown in Figure 4, a lower mold half (30) having a cavity (32) and ejector pins (34) is preferably preheated to a temperature of approximately 320 degrees Fahrenheit and a conventional release agent is applied as a coating to cavity (32). Cavity (32) has a planform shape and size that conforms to the shape and size of the friction material component that is to be fabricated. Next, approximately forty.percent (40%) of the required powdered mixture (36) necessary to produce the fabricated part is placed in cavity (32) and distributed evenly. It should be noted that if the powdered mixture (36) contains some discontinuous fibers to obtain desired frictional or wear characteristics the fibers preferably should have a length of no more than about one fourth the distance between opposing cell walls or the diameter of circular cells.
Figure 5 illustrates the next process step involving the placing of a pre-cut and expanded honeycomb reinforcement core (38) within mold cavity (32) and with honeycomb core (38) penetrating the distributed mixture (36) until contacting the lower surface of the mold cavity. Basically, the axes of the core cells are oriented at right angles to the lowermost surface of cavity (32). Afterwards the manufacturing process is

continued by placing the remainder of the required powdered mixture (3 6) necessary to produce the fabricated part in mold cavity (32) and distributing it evenly over honeycomb reinforcement core form (38) to thus completely fill all of the core cells. See Figure 6.
As shown in Figure 1, an upper mold half (40), also preferably pre-heated to approximately 320 degrees Fahrenheit, is next assembled to lower mold half (3 0) causing the lower surface of upper mold half punch feature (42) to contact the distributed full quantity of mixture (36) and cause it to become compressed. We prefer that the compression forces applied to mold halves (30 and 40) be sufficient to generate an isostatic compression pressure of approximately 600 pounds per square inch throughout mixture (3 6).
Next the interior of filled cavity (32) is vented to the atmosphere at l-minute, 2-minute, and 3-minute elapsed times following initial compression. Thereafter, the compression forces are preferably increased to a level that will produce an isostatic compression pressure of approximately 1200 pounds per square inch in the compressed mixture and that level of compression is preferably maintained for a period of approximately 2 minutes.
Lastly, the so-compressed and partially cured part is next ejected from the mold assembly using ejector pins (34) and is subsequently transferred to a curing oven. In the oven the part is heat cured by raising the friction material temperature linearly to approximately 300 degrees Fahrenheit over a 3 hour period and then maintaining the heated part at the 300 degree

Fahrenheit temperature for an additional 4 hours of process time. After cooling to ambient temperature the fabricated friction material part is ready for finishing and subsequent incorporation into the braking device or the like component for which it is intended.
An alternate honeycomb core reinforcement (24) may be seen by referring to Figure 15. Core (24) has adjoining, open ended cells defined by walls the same as core (22) depicted in Figures 1 through 9. Core (24) also has a facing sheet (26) attached to one end of its cell walls. Sheet (26) provides additional rigidity for reinforcement core (24).
A method for embedding the alternate honeycomb reinforced core (24) depicted in Figure 15 in a friction material matrix is illustrated schematically in Figures 16 through 18. As shown in Figure 16, a lower mold half (43) having a cavity (44) and ejector pins (45) preferably is heated to a temperature of approximately 320 degrees Fahrenheit and a conventional release agent is applied as a coating to cavity (44). Cavity (44) has a planform shape and size that conforms to the size and shape of the friction material component that is to be fabricated. Thereafter, reinforcement core (24) is placed in cavity (44) with facing sheet (26) engaging the bottom of cavity (24). It may be seen that the axes of the core cells are oriented at right angles to the surface of facing sheet (26) and to the lowermost surface of cavity (44). Thereafter, the manufacturing process is continued by placing the required friction material mixture (46) necessary to produce the fabricated part in mold cavity (44) and

distributing it evenly over honeycomb reinforcement core (24) to thus completely fill all of the core cells. See Figure 17.
Turning to Figure 18, it may be seen that upper mold half (47) , also preferably preheated to approximately 320 degrees Fahrenheit, is next assembled to lower mold half (43) causing the lower surface of upper mold half punch feature (48) to contact the distributed full quantity of mixture (46) and cause it to become compressed. Preferably the compression forces applied to mold halves (43 and 47) are sufficient to generate an isostatic compression pressure of approximately 600 pounds per square inch throughout mixture (4 6) .
Next the interior of filled cavity (44) is vented to the
atmosphere at one minute, two minute and three minute elapsed
times following initial compression. Thereafter, the compression
forces are preferably increased to a level that will produce an
isostatic compression pressure of approximately 1200 pounds per
square inch in the compressed mixture and that level of
compression is preferably maintained for a period of
approximately two minutes. Lastly, the so-compressed and
partially cured part is next ejected from the mold assembly using
ejector pins (45). Subsequently the part is transferred to a
curing oven tc be heat-cured by raising the friction material
temperature linearly to approximately 300 degrees Fahrenheit over
a three hour period and then maintaining the heated part at the
300 degree Fahrenheit temperature for an additional four (4)
hours of process time. After cooling to ambient temperature the
fabricated friction material part is ready for finishing and
subsequent incorporation into a braking device or like component

for which it is intended.
In Table 1 below we provide details of three examples of friction material matrix compositions that have been utilized in the fabrication of our improved reinforced friction materials having an embedded honeycomb core reinforcement (22 and 24). The mixture designated "Mix 1" has, when cured, a friction level suitable for avoiding thermal fade when used with glass fiber-reinforced composite honeycomb cores having an expanded density greater than about 8 pounds per cubic foot. The mixture designated "Mix 2" is satisfactory for use with honeycomb cores fabricated of sheet or foil aluminum (e.g., 5052 wrought aluminum alloy) and having an expanded density of at least about 5 pounds per cubic foot. The mixture designated -"Mix 3" includes some discontinuous carbon fibers which are desirable where increased wear or fade resistance is required. This mixture is suitable for use with glass fiber reinforced composite honeycomb cores having an expanded density greater than about 8 pounds per cubic foot. It has been found that where discontinuous fibers are added to a powdered mixture in the manufacture of a friction material part the fiber length preferably should be less than about one fourth the distance between opposing wall cells or of the diameter of the cells if they are round to ensure good fill of the honeycomb core walls. If the preferred fiber length is utilized good fill of the core cells will occur regardless of the percentage of discrete discontinuous fibers added to the mixture. All constituent values are given on a percentage parts by weight basis.

In dynamometer testing of various honeycomb core-reinforced friction materials it was observed that certain disc pad components incorporating honeycomb core reinforcements having an expanded density of less than about 5 pounds per cubic foot sometimes exhibited a tendency toward hairline cracking. To overcome the hairline cracking problem, we originated a hybrid disc brake pad in which the friction material with honeycomb core reinforcement is bounded at its planform edges and on one face by a different but compatible friction material. Figure 8 illustrates the resulting hybrid disc brake friction pad assembly (50) in which the friction pad component (52) bonded to steel base plate component (54) has an invwardly-situated principal friction material area (56) fabricated with an embedded low-density honeycomb core inserted within a cup or walled receptacle (58) of compatible friction material area. The friction material area (56) may or may not be centered within the pad component (52). Indeed, friction material area (56) may be laterally or longitudinally offset in pad component (52) and may occupy a

relatively small portion of the total area of pad component (52). The compatible friction material may or may not have a high thermal conductivity.
If a high thermal conductivity is desired, a semi-metallic
material may be utilized for the receptacle. Fabrication of a
hybrid disc brake friction pad assembly having a central friction
material area (56) fabricated with an embedded honeycomb core and
encased in a walled receptacle (58) may be accomplished utilizing
the following described process. A first mold for fabrication of
the central material area (56) is heated to a temperature of
approximately 230 degrees Fahrenheit. Next, approximately forty
percent (40%) of the required powdered mixture for the central
friction material area (56) is placed in the lower mold cavity
and distributed evenly. Thereafter, a pre-cut and expanded
honeycomb reinforcement core is inserted into the lower mold
cavity with the honeycomb core penetrating the distributed
mixture until contacting the lower surface of the lower mold
cavity. Subsequently, the remainder of the required powdered
mixture necessary to produce the central area (56) is placed in
the lower mold cavity and distributed over the honeycomb
reinforcement core form to completely fill the core cells.
Thereafter the mold upper half is assembled to the lower mold
half causing the lower surface of the upper mold half punch to
contact the full quantity of mixture and cause it to be
compressed. A compression force of approximately 200 pounds per
square inch is applied for approximately three minutes to make
the preform. This process is identical to that described

previously in Figures 4 through 7.
Thereafter, the so-made central friction material area (56)
is removed from the first mold. Subsequently, the central
friction material area (56) is placed in a second mold assembly
(72) having a planform of the final pad as may be seen by
referring to Figures 19 through 21. This mold (72) is preheated
to a temperature of 320 degrees Fahrenheit. The area (56) is
inserted into the central portion of lower mold half (74) of the
second mold and the mixture (55) comprising the walled receptacle
(58) is distributed evenly along the perimeter (57) of the area
(56) and across the top surface (59) of the area (56).
Subsequently, the mold upper half (76) is assembled to the mold
lower half (74) to cause a compression force to be applied to the
central area (56) and the mixture (55) forming the walled
receptacle (58). Preferably a compression force of approximately
1200 pounds per square inch is applied to a second mold for a
minimum period of two minutes. Thereafter the so compressed and
partially cured part is ejected by pins (78) from the second mold
assembly (72) and transferred to a curing oven where it is heat
cured.
An example of a satisfactory semi-metallic, non-reinforced friction material for a hybrid disc brake friction pad assembly is given in the Table 2 which follows as "Mix 4". Again,, all constituents are stated on a percentage parts by weight basis.

Figure 9 illustrates the present invention as applied to a drum brake friction shoe assembly designated (60) . Assembly (60) includes an arcuate shoe table (62) joined to and supported by a perpendicular shoe web (64). A friction shoe component (66), having an arcuate under surface that corresponds to and mates with the upper surface of arcuate shoe table (62), is secured to the upper surface of shoe table (62), by an interface adhesive (68) . Other known fastening techniques, such as the use of rivets or the like, may be utilized to join friction shoe (66) to shoe table (62) in preference to use of an adhesive. In the brake shoe construction illustrated in Figure 9 it is important that friction shoe (66) be fabricated using. the reinforced friction material of our invention. The presence of the embedded honeycomb core reinforcement in the friction material matrix is clearly shown in Figure 9.
Figures 10 through 13 are provided in the drawings to illustrate some of the different cell cross-sectional geometries that are obtainable in commercially available honeycomb core reinforcement materials. The illustrated honeycomb core fragments are designated 70, 80, 90, and 100, respectively. Generally, as stated above we prefer to use honevcomn cores with

core cell sizes in the range from as little as approximately 1/16 inch (minimum distance measured from cell wall to opposite cell wall in the expanded condition) to as much as 1 inch. Also, as previously indicated, we basically prefer to define the incorporated or embedded honeycomb reinforcement core in terms of its bulk (expanded) density which typically ranges from as little as approximately 2 pounds per cubic foot to as much as approximately 20 pounds per cubic foot and which is influenced significantly by the core cell wall thicknesses, by the density of the particular material from which the core cells are configured, and by the core cell cross-sectional dimensions.
The new reinforced friction material of this invention preferably does not contain fibers, either discontinuous or continuous, as a reinforcement. This is especially achievable in those instances wherein the honeycomb core reinforcement is made of a metal (e.g., aluminum). Even in cases wherein the honeycomb core reinforcement is made of a glass fiber-reinforced or carbon fiber-reinforced material such as a glass fiber-reinforced phenolic composite or a carbon fiber-reinforced polyimids composite the quantity of fibrous material in the fabricated friction material product is small in comparison to a conventional fiber-reinforced friction material. For instance, a honeycomb core reinforced friction material fabricated using Mix 2 of Table 1 above utilized an embedded honeycomb core reinforcement made of 27.6% glass fiber by weight and 72.4% of phenolic resin by weight. Because the reinforcement core comprised only 10.8% by weight of the completed friction

material, the actual fibrous material content of the reinforced friction material was only 2.98% by weight. This level of fiber content is significantly lower than the typical 20% or more fiber content of known fiber-reinforced friction materials.
The reinforced friction material made in accordance with the method of this invention is processed without the necessity of having to uniformly mix discontinuous fibers with powder (particulate) mixture constituents except where small amounts of such fibers are utilized to obtain desired frictional or wear characteristics, and thus avoids a major cause of manufacturing quality fluctuation. A substantially fiber-free mixing procedure is a much more efficient mixing process and results in a significantly improved consistency of quality.
Also, in wear-resistance testing to date the new reinforced friction material has shown considerably lower wear rates of 0.07% compared to 0.35% for a fiber-reinforced friction material under the same test conditions.
It is generally understood that the contact stiffness between the friction material and the rotor or drum affects the occurrence of brake noise. In order to eliminate or reduce the propensity of brake noise, it is often necessary to adjust the stiffness of friction material to an optimum value. However, for conventional friction materials, this essentially means reformulation of the materials and may result in other adverse consequences. The current invention successfully solves this problem by incorporating honeycomb cores into friction materials. Once a mixture has been formulated for a particular application, the stiffness of the pad can be changed by adjusting the

stiffness of the reinforcement core to avoid brake noise. The frictional characteristics of the pad will remain almost unchanged because the cured mixture covers most of the contact surface area.
Lastly, in conventional fiber-reinforced friction materials an uneven distribution of fibers often results in uneven brake rotor or brake drum wear treatment manifest by surface grooving. In comparison, Krauss and inertia dynamometer testing of the new reinforced friction material of our inventions was noted to result in very smooth brake rotor wear.
Other suitable materials, component shapes, and component sizes may be utilized in the practice of this invention.
Since certain changes may be made in the above-described system and apparatus not departing from the scope of the invention herein and above, it is intended that all matter contained in the description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

WE CLAIM:
1. A reinforced friction material having two distinct phases joined by a
cured binder, and comprised of:
a honeycomb core reinforcement having multiple, adjoining, open-ended cells separated by cell walls and constituting a three-dimensional continuous phase:
mixed friction particles and filler particles contained within said reinforcement open-ended cells and constituting a three-dimensional discontinuous phase and
cured organic polymer binder binding said mixed friction particles and filler particles and said reinforcement into a unitary part by covalent bonds and electrostatic bonding.
2. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of aluminum alloy.
3. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of glass fiber-reinforced cured phenolic resin.
4. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of glass fiber-reinforced cured polyimide resin.

5. The reinforced friction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of carbon fiber-reinforced polyimiede resin.
6. The reinforced friction material as claimed in claim I wherein said honeycomb core reinforcement is comprised of an iron alloy.
7. The reinforced friction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of an aramid material.
8. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of a thermoplastic material.
9. The reinforced friction material as claimed in claim 1 wherein said honeycomb core reinforcement is comprised of a ceramic material.
10. The reinforced fiiction material as claimed in claim 1 wherein said honeycomb core reinforcement open-ended cells each have a cell cross-sectional planform selected from the group comprised of triangular, square, rectangular, trapezoidal, rhomboidal and hexagonal cross-sectional planforms.

11. The reinforce friction material as claimed in claim 1 wherein said honeycomb core reinforcement has a bulk (expanded) density in the range of from approximately 2 pounds per cubic foot to approximately 20 pounds per cubic foot.
12. The reinforced friction material as claimed in claim 1 wherein said honeycomb core reinforcement has a facing sheet attached to one end of said cell walls.
13. The reinforced friction material as claimed in claim 1 wherein said mixture of friction particles and filler particles also includes discontinuous fibers.
14. The reinforced friction material as claimed in claim 13 wherein said discontinuous fibers have lengths less than about one-fourth the distance between the opposing cell walls of said honeycomb reinforcement core or the diameter of the cells if they are circular.
15. The reinforced friction material as claimed in claim I wherein said opposing cell walls of said honeycomb core reinforcement are spaced apart a distance from about one-fourth inch to about one inch.
16. The reinforced friction material as claimed in claim 1 wherein said cell walls of said honeycomb core reinforcement have a diameter ranging from between about one-sixteenth inch to about one inch.

17. The reinforced friction material as claimed in claim 1 further
coraprisisng;
a base element having structural rigidity;and
securing means for securing said reinforced friction material to said base element.
18. The reinforced friction material as claimed in claim I wherein said honeycomb core reinforcement is non-metal.
19. A method of manufacturing a reinforced friction material claimed in any one of the preceding claims, comprising the steps of:
placing and evenly distributing a first measured quantity of a friction material mixture comprised of friction particles, filler particles, and binder particles in a mold cavity having a planform corresponding to the planform of said friction material shape;
Placing a honeycomb core reinforcement in said mold cavity with complete penetration of only a lower portion of said reinforcement through said evenly distributed fiiction material mixture.
placing and evenly distributing a second measured quantity of said friction material mixture in said mold cavity to completely fill the upper portion of said honeycomb core reinforcement; and
comprising said placed and evenly distributed fiiction material mixtures to an elevated isostatic pressure and elevating the temperature of said placed and evenly distributed fiiction material mixtures to form said reinforced fiiction material shape.

20. The method as clamed in claim 19 wherein said honeycomb core reinforcement placed in said mold cavity in penetrating relation to said friction material mixture has a bulk (expanded) density in the range of from approximately 2 pounds per cubic foot to approximately 20 pounds per cubic foot.
21. The method as claimed in claim 19 wherein opposing cell walls of said honeycomb core reinforcement are spaced part a distance of from about 1/16 inch to about 1 inch.
22. The method as claimed in claim 19 wherein said cell walls of said honeycomb core reinforcement have a diameter ranging from about 1/16 inch to about 1 inch.
23. A reinforced friction material, substantially, as hereinabove described and illustrated with reference to the accompanying drawings.
24. A method of manufacturing a reinforced friction material, as hereinabove described and illustrated with reference to the accompanying drawings.

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Patent Number

188557

Indian Patent Application Number

435/MAS/1995

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

18-Jul-2003

Date of Filing

10-Apr-1995

Name of Patentee

WAGNER ELECTRIC CORPORATION

Applicant Address

1001 FANNIN STREET, SUITE 4000, HOUSTON, TEXAS 77002

Inventors:

#	Inventor's Name	Inventor's Address
1	YONGABIN YUAN	118 ELAINE DRIVE, WINCHESTER, VA 22602
2	STANLEY FRANK KULIS JR	284 DUNDRIDGE DRIVE, WHITE POST, VA 22663,
3	TIMOTHY FRANKLIN MERKEL	784 JOHNSTON COURT, WINCHESTER VA 22601

PCT International Classification Number

F16D 69/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA