Reinforced friction material

An improved reinforced friction material is comprised of a cured friction material mixture of friction particles, filler particles, and binder particles, and has a embedded honeycomb core reinforcement whose individual cells are filled with and bonded at the cell walls to the cured friction material mixture by a novel manufacturing method.

FIELD OF THE INVENTION 
This invention relates generally to friction materials useful for 
incorporation in various brake assemblies and other friction-producing 
devices, and particularly concerns novel friction materials having an 
embedded honeycomb core for reinforcement. 
BACKGROUND OF THE INVENTION 
The us 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. Pat. 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. Pat. 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. Pat. No. 4,278,153 issued in the name of Venkatu discloses a brake 
disc construction having a copper or copper-plated metal honeycomb core 
reinforcement that is filled with a powdered friction material, normally 
comprised of powdered metals and including powdered copper. The powdered 
friction material is subsequently sintered at an elevated temperature in 
the range of 1,800 to 2,000 degrees Fahrenheit to form a unitary structure 
that is made up essentially of single phase, metal-to-metal bonded 
material resulting from solid state fusion of the mass. 
U.S. Pat. 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 aramide fibers, mineral fibers, 
and steel fibers reinforcing a hardenable binder. 
U.S. Pat. No. 4,384,640 issued in the name of Trainor et al. discloses a 
friction composition 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. Pat. 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 fibers and organic fibers as reinforcements in a mixture 
having fillers and a binder. The organic fibers are at least partially 
composed of a cross-linkable, fusible type such as acrylic or modacrylic 
fibers. 
U.S. Pat. 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 (polytetrafluoroethylene) 
fibers in yarn form. See also U.S. Pat. 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. 
Pat. 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. 
Also, see U.S. Pat. Nos. 3,673,058 and 3,790,654 issued in the names of 
Jackson et al. and Bagley, respectively, for disclosures of apparatus and 
methods for manufacturing honeycomb core materials. 
Our 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 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 may also 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 completely 
filled 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 and 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 also believed that the reinforced friction material of this invention 
may also 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.

DETAILED DESCRIPTION 
FIG. 1 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. 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. 
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 
FIGS. 1, and 8 through 10, for example). Other available core cell 
cross-sectional configurations are illustrated and described in connection 
with FIGS. 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 20 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 1/16 inch and 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 in the 
friction material matrix is illustrated schematically in FIGS. 4 through 7 
of the drawings. As shown in FIG. 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. 
FIG. 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 36 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 FIG. 6. 
As shown in FIG. 7, the mold upper half 40, also preferably pre-heated to 
approximately 320 degrees Fahrenheit, is next assembled to lower mold half 
30 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 36. 
Next the interior of filled cavity 32 is vented to the atmosphere at 
1-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 at 
least approximately 2 minutes. 
Lastly, the so-compressed and partially heated pre-form 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 
pre-form at the 300 degree Fahrenheit temperature for an additional 4 
hours of process time. After cooling to ambient temperature the fabricated 
friction material form is ready for 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 
FIG. 15. Core 24 has adjoining, open ended cells defined by walls the same 
as core 22 depicted in FIGS. 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 FIG. 15 in a friction material matrix is illustrated schematically in 
FIGS. 16 through 18. As shown in FIG. 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 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 FIG. 17. 
Turning to FIG. 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 hold halves 43 and 47 are sufficient to generate an isostatic 
compression pressure of approximately 600 pounds per square inch 
throughout mixture 46. 
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 to 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 cells. 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. 
TABLE 1 
______________________________________ 
Constituent Mix 1 Mix 2 Mix 3 
______________________________________ 
Graphite Particies 
5.32 6.14 4.93 
Brass Chips and Particles 
2.39 2.76 2.21 
Cashew Nut Shell Resin Particles 
5.46 8.52 5.06 
Carbon Black Particles 
1.30 1.50 1.21 
Rubber Peel Particles 
5.56 8.52 5.15 
Coke Particles 19.43 15.16 18.01 
Barite Particles 46.23 36.47 42.86 
Aluminum Oxide particles 
3.46 0.25 3.21 
Phenolic Resin Particles 
10.85 20.68 10.05 
Short Carbon Fibers 
0.00 0.00 7.31 
Total 100.00 100.00 100.00 
______________________________________ 
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. FIG. 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 
inwardly-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 FIGS. 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 FIGS. 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 the 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 is given in the Table 2 which follows as "Mix 4". Again, all 
constituents are stated on a percentage parts by weight basis. 
TAELE 2 
______________________________________ 
Constituent Mix 4 
______________________________________ 
Mineral Particles 9.0 
Rubber Peel Particles 
1.0 
Coke Particles 4.0 
Ferrous Particles 57.0 
Graphite Particles 
17.0 
Phenolic Resin Particles 
12.0 
Total 100.0 
______________________________________ 
In all cases the basic matrix formed from the mixture components, including 
organic, inorganic, and metallic constituents, are held together by an 
organic thermosetting polymer system (e.g., phenolic resin). The polymer 
binder melts, flows, and forms a three-dimensional network among the 
constituents utilizing co-valent bonds. In addition, electrostatic bonding 
plays a smaller part in the bonding process of the matrix. The binder 
resin system bonds directly to reinforcement cell walls causing the fiber 
honeycomb core material to be the primary reinforcing material. 
In the new reinforced friction material construction the honeycomb core 
material constitutes the product continuous phase with the polymer binder 
being the discontinuous phase. In comparison, in a conventional 
non-asbestos fiber, non-metallic fiber friction material the reinforcing 
fibers constitute a discontinuous phase held together by a continuous 
phase binder. The advantages of the new system include increased 
three-dimensional structural strength or rigidity in comparison to the 
known polymer-bound friction materials. 
FIG. 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 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 FIG. 9 brake shoe construction 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 FIG. 9. 
FIGS. 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, we prefer to use honeycomb 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 very much 
influenced 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 polyimide 
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, and 
thus avoids a major cause of manufacturing quality fluctuation. A 
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 the 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 
invention 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. Also, the reinforced friction 
material of this invention may be used in drum brake assemblies for 
automobiles, trucks, buses and off highway vehicles as well as in the disc 
and drum brake assemblies described hereinabove. Furthermore, the 
reinforced friction material of this invention may be utilized in 
industrial brake and clutch applications such as elevator brake 
assemblies, lawn mower vehicle brake and clutch assemblies, etc. 
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.