Note: Descriptions are shown in the official language in which they were submitted.
~S~65
Back~round of the Invention
This invention relates to composite materialsO More
specifically, this invention relates to composite friction mater-
ials which exhibit high, stable, coefficients of friction over
a wide temperature range.
The elastomeric materials heretoEore proposed for use
as materials have generally proven to be unsatisfactory when
exposed to high ambient working temperatures such as encountered,
for example, in clutch and brake applications in heavy duty
service vehicles. Typically, such materials have been based on
heat-hardenable resins suchi as phenol-aldehyde resins which tend
to heat-decompose under the high peak and bulk temperature con-
ditions created by the sustained and/or heavy loading forces
experienced in the clutch and brake systems of these vehicles
while operating. As a result of this decomposition, the physical -
properties of these materials typically deteriorate, and the
consequent disintegration of the material and dispersal of the ;
products of heat decomposition generally interfere with the
functioning of the friction unit. Furthermore, many times after
friction material comprising a partially heat-decomposed heat- `
hardenable resin has cooled, the material will exhibit incon-
sistency with respect to coefficient of friction.
These conditions, as well as other problems associated
with these and similar friction materials~ result in a loss of
efficiency in the friction unit and unreliability in the service
vehicle, which is highly undesirab]e.
Many attempts have been made to obviate the problems `
associat~d with the elastomers in general use as friction mater-
ial bases. Many different resins have been experimented with,
in attempts to obtain a friction material which possesses a high,
-2-
,, :: , , .: :, ::
stable coefficient of friction over a wide temperature range.
Modification of the heat-hardenable resins with other polymeric
materials has been attempted. ~lany of these friction material
formulations have not performed ~ell. Other formulations have
required multi-step procedures which are costly in terms of
labor and frequently in terms of the material used in these forrn-
ulations.
Importantly, also, many of these known friction mater-
ials require a bonding agent to affix thern to the backing plate
or "core" portion of the friction element. This requirement
severely restricts Jhe scope of the molding methods and mold
configurations employable in forming these friction eleme'nts.
In injection molding, for example, the bonding agent is subject
to scuffing during the molding process, which deactivates or `~
destroys the bond and renders this molding process useless with
these friction elements. In general 5 where bonding agents must
be utilized, only compression molding and relatively simply mold
configurations can be employed in the process of molding the
friction element.
In order to obtain a friction material with a usefully
high coef'ficient of f'riction which is stable over a wide tempera-
ture range, the industry has most usually used nonresilient
inorganic friction materials such as sintered bronze. Although
the friction characteristics of this and similar metallic mater-
ials have been generally satisf'actory under high temperature
conditions, the high modulus or lack of resiliency of' these
materials and their resultant inability during operation to
conform to the friction element mating surface and absorb adequate
energy result in relatively high wear rates and shortened life.
Furthermore, great care must be taken in the type and viscosity
-- ~0~5~65 ~
of oil used in conjunction with such ~riction materials during
use to ensure that the desired coefficient of friction is not
impaired.
It has been determined by actual tests that the
bronze clutch material, when employed in the high load oil- -
cooled clutch environment of a transmission for a heavy
duty earthmouing vehicle, exhibited some measurable difference
in its frictional properties as a function of viscosity
grade of the lubricant. It was theorized that at least
a part of the energy absorption during the engagement cycle
between the friction plate and the reaction plate was through ;
shear of the fluid as well as the boundry lubrication or
intimate contact between the clutch plate and reaction
plate. It was further recognized that great advantage coul~
be obtained by maintaining the oil film thickness to a
minimum dimension in order to permit more of the energy o~
engagement to be absorbed by shear in the oil film and that
a further advantage would be gained by sustaining such thin
film in the order of a few microinches during a longer
portion of the engagement aycle. Several well known
principles of fluid mechanics were considered to aid in this
:,
development. For example, the oil film thickness between
a rotary friction plate and a stationary substantially
,; .
flat reaction plate is a function of the radius of curvature
or size of the protuberances or asperities in the friction
material under a given load. Accordingly, the smaller
the asperities in the surface of the friction plate, the
thinner the oil film thickness~ It is also known that
the thinner the oil film thickness, the greater rate of -
shear and, therefore, the greater shear force and energy
that the oil film is capable of absorbing. Accordingly,
~ -4-
.. , , . ~ ;,. ., , ,, . . . , ,,: .
~ S~65
a great plurality of such asperities in the surface of the
~riction plate produces ~
~;
-4a-
04~65
,
greater fluid wedging ef~ect of the oil filrn as it is squeezed
between the multitude of as?erities and the reaction plate to
produce a substantial drag on the friction plate. Furthermore,
the greater the amount of oil film in thin film shear, as
discussed above, the greater the energy absorption. Accordingly,
the substantially large number of asperities in the surface of
the friction plate results in a greater amount of oil being
retained over the entire surface area of the plate due to the
trapping effect and cavitat~on of oil on the trailing sides of " -
the asperities over the surface area between the friction material
plate and its mating reac~ion plate. It is further recognized
that the greater the real viscosity or internal resistance to
flow of fluid in contact between the plates, the greater the
energy absorption obtainable in the thin film shear. Such real
or developed viscosity during the engagement cycle is, of course, ; ~-
enhanced by the substantial number Or asperities through which : -
the engagement pressure is transmitted to the oil fi:Lm in shear.
It is also known that the g~eater the relative motion between
the friction plate and the reaction plate, the greater the shear
and~ again, the greater ene~gy absorpkion obtained. In using ~ ~
the above-discussed simple ~luid mechanics principles, the ;
problem was presented of how best to maximize energy absorption
between a pair of friction plates through a fluid film with the
greatest reliability and over substantially the entire range of
the engagement cycle.
Accordingly J it is an object of the present invention to
provide an improved friction coupling which utilizes an improved
friction material capable of cooperating wi~h a fluid for pro-
ducing a thin fluid film between it and the reaction member wherein
a substantial portion of the energy of plate engagement is
... . . . . ..
,,, . , ;: ., : . . . . .
. .
1~)45~6S
absorbed in shear of the fluid film for greater wear resistance,
temperature stability and a higher coefficient of friction
than heretofore obtainable.
Brief Summary of the Invention
According to one aspect of the invention there
is provided a friction coupling comprising: a rotatable
.friction plate formed of a matrix of a relatively soft
elastomeric material providing a friction surface and selected
from the group o~ elàstomeric materials consisting of poly-
acrylate, silicone, fluorosilicone, chloroprene, acrylonitrile,
urethane, and hexafluoropropylene-vinylidene fluoride co-
polymer and mixtures thereof; a reaction plate of relatively
rigid non-compressible material providing a mating surface
for selective rotational frictional engagement with said
friction surface of said friction plate; a plurality of .
discrete particles of a vitreous or ceramic material inter-
mixed with and dispersed throughout said elastomeric material
to provide relatively high modulus particles in said friction
surface with said matrix reboundably deflecting to permit
at least partial recession of the more prominently extended -
particles into the friction surface of the matrix to ensure
ma~imum conformability to said mating surace and uniform
distribution of engagement pressure over the entire surface
area of the plates; and a supply of fluid provided between
said plates with the fluid hydrodynamically wedging ~etween
the particles and the mating surface of the reaction plate
duriny relative rotation of the plates for developing and
sustaining a film of separating fluid over the particles
that produces a viscous drag upon the friction plate so
as to cause substantially all of the energy of plate
engagement to be absorbed in shear of said fluid film until
.
-6-
' ~=-;,. :
.i( ~, .
` ~1)4S~)biS
just prior to complete engagement o~ the plates.
~ccording to another aspect of the invention . .:
here is provided a friction coupling comprising~ a rotatable :- .
friction plate formed of a matri~ o~ a relatively so~t
elastomeric material providing a friction surface; a reaction
plate of relatively rigid non-compressible material providing :.
a mating surface for selective rotational frictional engage-
ment with said friction surface of said friction plate; .
a plurality of discrete particles of a vitreous or ceramic
material intermixed with and dispersed throughout said .
elastomeric material to provide relatively high modulus
particles with corresponding voids therebetween over substan-
tially the entire surface area of said friction surface with -~
said matrix reboundably deflecting to permit at least partial
recession of the more prominently extended particles into
the friction surface of the matrix and substantial elimination .
of said voids to ensure maximum conformability to said mating
surface and uniformed distribution of engagement pressure :
over the entire surface area of the plates; and a free flow ~'
supply of ~luid provlded between said plates with the fluid
2n during movement of the plates toward each other hydrodynamic- :
ally wedging between the particles and the mating surface of
the reaction plate during relative rotation of the plates
for developing and sustaining a film of separating fluid
over the particles that produces a viscous drag upon the
friction plate so as to cause substantially all of the
energy of plate engagement to be absorbed in shear of said
fluid film until just prior to the disappearance of said ;
parti~cles into the matrix for permitting complete engage~
ment of the entire surface areas of the plates.
-6a- ..
..
~i, "1
~45(~5
~ n advantage of the present invention, at least in
preferred forms, is that it can provide an improved friction
coupling in which the friction plate is formed of a relatively
soft elastomeric material and has intermixed therewith a
plurality of relatively high modulus particles in the surface.
thereof which cause a hydrodynamic wedging of the fluid to
establish a load absorbing film of separating fluid between
the friction plates for maximi~ing the absorption of energy
during plate engagement.
The friction coupling may thus utilize a friction
material composition with high dynamic and static coefficients
of friction over a wide temperature range, and which can
readily be bonded to a metal core material.
The friction material composition may also be
injection or compression molded, in preferred embodiments, and
may be molded in conjunction with complex mold configurations.
Furthermore, the friction coupling may thus utilize
conformable, long-wearing friction material composition with
a high, stable coefficient of friction over a wide temperature
range.
Broadly, the composite friction material utilized in
this invention, at least in the preferred embodiments, comprises
a compounded elastomeric matrix in which are suspended minute
particles of a vitreous or ceramic friction-producing
agent. The fluoroelastomer matrix has excellent pro-
perties of thermal stability, and at the same time provides a
relatively low modulus resilient matrix which permits the
friction material to conform readily to inherently rapid changes
between it and its mating surface, thereby distributing dynamic
stresses and energy absorption over a much larger true friction
surface area than is permitted with high modulus metallic or
~s~s
other non-resilient materials.
Maximum energy absorption rates of from about 3 to
about 5 HP/in of fluoroelastome-r friction material are typical.
In comparison with the high modulus materials, such a low
modulus matrix significantly increases the load-carrying
capabilities of the friction element of which it is a part,
and further, possesses superior wear characteristics when
compounded with high modulus asperities as herein disclosed.
The high modulus vitreous or ceramic particles
are compounded with the fluoroelastomer in sufficient
quantities to produce a relatively high concentration ~5', .
of these particles on the frictional surface of the fluoro-
elastomer matrix. These particles further serve to
strengthen the support matrix and-lessen compression set or
permanent deformation under applied loads. ~ -
The compounded friction material is then applied to ;
the core of the friction element, for example as disclosed in
U.S. patent no. 4,036,668 by William D. Brandon, issued on
July 19, 1977, of common assignment herewith.
`
~''; ' ~'-
' ,,~ '
`.~
~ '
~'''.'. "'
S~65
When such improved friction material is utilized
in a disc-type oil-cooled transmission clutch or brake
environment for frictional engagement with a reaction plate
of relatively rigid noncompressible material, the particles
create a hydrodynamic wedge in the oil passing between the
friction material and the reaction plate with the microscopic
size of the particles producing a relatively thin oil film.
This increases the viscosity of the oil film fully to support
the load imposed between the friction plate and the reaction
plate prior to their complete engagement. Both the viscous
shear of the fluid and the pressure drag created by the
hydrodynamic wedging of oil ahead of the particles and the
cavitation behind the particles contribute to the frictional
force. This makes it possible to use the oil film to achieve
dynamic frictional braking exclusive of the elastomeric
material in the frictional surface during the major portion
of the engagement cycle which produces greater wear
resistance and improved temperature stability with a higher
coefficient of friction than previously achieved with
conventional friction materials.
Description of the Drawings
FIG. 1 is a photomicrograph tat 500X magnification)
of the surface of material according to the invention after
this surface has been "worn in". The rod-like particles
are clearly seen with the worn flat surfaces thereon apparent.
FIG. 2 is a photomicrograph (at 500X magnification)
of another sample of material according to the invention.
The particles are noted to have flattened upper surfaces
produced upon "wearing in" of the material.
FIG. 3 is a photomicrograph (at 200X magnification)
of a cross section through the improved friction material
_y_
1~)45~i5
utilized in the present invention showing a plurality of
particles of vitreous materlal dispersed throughout the -
relatively soft elastomeric metrix and protruding above
the surface of the matrix.
FIG. 4 is a photomicrograph (at 500X magnification~
of another cross sectional view through the improved friction
material of the preceding FIGS.
FIG. 5 is a force curve graph representing a
conventional clutch or brake ~peration under simple conditions
of engagement.
FIG. 6 is a graph showing the force curve under
conditions of clutch or brake operation wlth the improved
friction material utilized in the presPnt invention operating
under a microelastohydrodynamic condition in conformance
with the principles of the presentiinvention.
FIG. 7 iS a greatly enlarged sectional view through
the improved frictlon material disposed adjacent to a ~ -
substantially flat reaction plate with a relatively thin -;
energy absorbing oil film produced therebetween.
FIG. 8 is a central vertical cross section through
a typical disc-type oil-cooled clutch or transmission brake '
employed on relatively heavy earthmoving vehicles with the
improved friction material shown utilized in combination
with a continuous flow of hydrodynamic braking fluid.
Detailed Description of the Invention
.. . .. .
This invention utilizes an elastomer based material
having vltreous or ceramic particles dispersed therethrough.
In the described embodiment a fluoroelastomer is used;
however, it will be apparent that other elastomers such
as polyacrylate, silicone, fluorosilicone, chloroprene,
acrylonitrile, or urethane may be used without departing
-10- `;'
; .: . . .
o~s~s
from the spirit of the present invention. This composite
material exhibits tensile strengths comparable with the
elastomers alone, but however exhibits better set and stress
relaxation resistance than the fluoroelastomers alone.
The fluoroelastomers useful in this invention
are exemplified by Viton E60C (Trade Mark), a copolymer
of hexafluoropropylene and polyvinylidene Eluorid~ which
is commercially available from E. I. duPont, Inc.,
Wilmington, Delaware, and Fluorel FC2170 (Trade Mark),
commercially available from the 3M Company of Minneapolis,
Minnesota. Preferably, Viton E60C or Fluorel FC2170 are
employed to form the matrix of the friction material.
To form the composite material of the invention,
the fluoroelastomer has admixed therewith particles of a
relatively hard vitreous or ceramic material. These
particles are preferably in the form of very small beads,
fibers or other irregular shapes.
Although the useful size of these particles may
vary somewhat according to the nature of the material and
other factors, fiberglass particles of from about .0001"
to about .OU5" in diameter, and preferably about 0.0005"
in diameter, will yield the desired results. Such particles
advantageously have a length to diameter ratio of from
about 3 to about 100. The fiberglass or other particles
may also be compounded in the form of chips, fibers,
spheres or other con~enient shapes, although fibers are
generally preferable.
The particles are compounded with the fluoroelastomer
at a rate sufficient to give and maintain a high surface
concentration of particles in the finished Eriction facing.
Preferably, about 20 to about 503 by weight of fiberglass
5~
particles to about 30 to about 50~ by weight of fluoroelastomer
are admixed to provide a randomly irregular mlcroscopic surface
finish on the friction material. It may in some instances,
however, be desirable to exceed these proportions, depending
on the frictional characteristics desired in the finished
material.
It is contemplated that carbon black will be in-
corporated into the fluoroelastomer, conveniently at the
same time or prior to the time the vitreous or ceramic
particles are incorporated. This additive is preferably
added in amounts of about 12 to about 30~ by weight of carbon
black to about 30 to about 50~ by weight of fluoroelastomer.
Additionally, accelerators, stabilizers, and curing agents,
inter alia, commonly used in fluoroelastomer products, will
usually be compounded with the fluoroelastomer.
The vitreous or ceramic particles, carbon black,
and other additives are incorporated into the fluoroelastomer
by eonventional mixing techniques, for example, in a Banbury
mixer. Ideally, the particles should be concentrated near
the surface, or the frictionally active portion, of the
fluoroelastomer matrix. However, in practacality this is
difficult to achieve, and satisfactory results are obtained
by intimately incorporating the particles through the ;
fluoroelastomer to obtain a random orientation of the
particles through the matrix. -
The fluoroelastomer may be bonded to a core of
steel or other metal by the process of U.S. Patent No. 4,036,668
noted above. Broadly, this proeess comprises incorpor-
ating CaO into the fluoroelastomer prior to euring, and
then at high tempexatures curing the fluoroelastomer in
pressed contact with the core material. Conveniently, the
~ -lla-
~SC~65
CaO may be incorporated into the fluoroelastomer at the same
time as are the particles.and other additives noted above.
Conventional molding techniques, such as compression,
transfer or injection molding, are utilized for forming the
fluoroelastomer/backing plate friction element. In applying
the friction material to the backing plate of the friction
element, it is usually desirable to apply the friction material
to the plate in an amount sufficient to obtain a finished
thickness of
:
. . .
,
-llb-
:` ~0450~5
friction material of from about 0.020 to about 0.250 inches,
especially in applications where the material is utilized in
clutches.
The friction material of this invention exhibits
a high, stable, dynamic coefficient of friction through a
wide range of sliding speeds and normal loads against a wide
variety of opposing faces and finishes. For example, dynamic ;
friction coefficients (~D ) of from about 0.14 to about 0.06 -
at from about 2,000 to 11,000 ft/min sliding speed and from
about 50 to about 680 psi of face pressure on gross area
typically can be expected in friction elements comprised
of ~he friction material of this invention.
Additionally, good static ("breakaway-") coefficients
of friction from about 0.17 to about 0.26 are characteristic
of this fluoroelastomer friction material.
The friction material of this invention is capable
of operating against mating surfaces of a variety of types,
for example, hard or soft steel, cast iron~ sintered metals,
and ground, deburred or lapped surfaces. However, the mating
surface finish may adversely affect the friction characteristics
of the friction material if this surface is too roughly or
too finely finished. Generally, a mating surface finish
of about 10 to about ~5 mu will result in satisfactory
performance of the friction material.
The fluoroelastomer friction material of this
invention is further characterized by low wear and dimensional
stability during extended dynamic operation. Furthermore,
with properly modulated engaging pressure, the material
exhibits a relatively flat torque curve that "wrings in" ;
about 10-50% above the dynamic torque. ;
-12-
~s~s
The friction material Or this invention will respond
accordlng to test results over a wide operating surface tempera-
ture range even up to about 680F. In general~ the material can
be expected to maintain optimum response levels at bulk temper-
atures below about 475F; i.e., where the average surface tem-
perature Or the friction material bet~Jeen operations Or the
friction element is belo:w about 475F. Maximum peak temperatures,
however, may be as high as from about 5600F to about 680F before
performance Or the friction material is substantially arfected.
In general, effective performance of the friction mater- -
ial contemplates oper2tion Or the friction element under oil
cooled operating con~i~ions. However, a much wider selection
of oils may be effectively employed with the chemically inert ~-
fluoroelastomer friction material than with, for example, bronze.
In preparing friction elements utilizing the friction
material of this invention, it will generall~ be found that after
demolding, few if any of the vitreous or ceramic particles will be
present on the frictional surface of the material. The thin elas-
tomer coating covering the particles must therefore be worn off to
expose the particles and hence to obtain a stable coefficient of
friction for the element. This may either by done in_situ, allowing
the rubber coating to be worn off during an initial break-in period
of the friction element in the service vehicle, or by pre- ;~
grinding of the friction material before installation Or the
element. The amount of matrix material which must be removed
to obtain a desirably stable coefficient of friction ror the
material as a whole ~lill of course vary according to the specific ~,~
formulation. Ho~lever, it is generally advantageous to suffic-
iently expos~ a ma~or portion Or the underlying particles to a
point where these particles are in contact with the mating
surface.
.
-13- `
., . : . . .
- 1~45~ 5
During early use, these particles are ground to a
point where they appear to be well-worn, as shown in FIGS. 1
and 2, to obtain a stable coef~icient of friction. The
particles are mechanically held in the matrix in nonbonded
relation in order to enhance the noncompressive setting
characteristic of the material. -~
The following examples are provided only to further
illustrate specific friction material compositions of this
invention and pertinent frictional characteristics thereof,
without limiting the invention in any manner:
Example 1
Ingredients Amount (Parts by Weight) Size
!
Viton E60 100 parts
Type E Fiberglass 110 parts 0.0005"
diameter
Carbon Black 60 parts
Accelerators
Stabilizers ) Minor amounts
Curing Agents
.... ..
CaO ) 5 parts `
The abo~e ingredients were compounded by mixing
in a Banbury mixer (Trade Mark) mixer to achieve an even
dispersion of the additives into the fluoroelastomer matrix,
with random orientation o~ the glass particles. The mixture
was applied to a steel backing plate and pressed to this
plate into the desired pattern under about ? . soo psi. The
mixture then was cured for 30 seconds at 390F. Sufficient
mixture material was applied to the plate to give a thickness
of material, when cured, of 0.50 inches/face. The cured
elastomer and backing plate, i.e., clutch disc, were then
postcured at 450F for 16 hours.
-14-
.
5~6S
It ~as found tha~ the friction material possessed a
Shore A Hardness of 90 - 95, and an ultimate tensile strength
of 1,900 to 2,100 psi. The clutch friction element made by the
process of Example 1 ~1ras then subjected to a wear test in an
earthmoving vehicle transmission comprising 220,000 cycles,
from third speed reverse to third speed forward. 0. oo8 inches
of ~ear was observed per friction material ~ace element at the
conclusion of this test. The friction material was found to
have an excellent thermal stability up to l175 F (bulk), and
680 F (peak).
~x~m~le 2
Full Scale Clutch Test Results
Friction Material As in Example 1
Size O.D. - inches 12.25
Area/Face - inches 31 --
Faces/Clutch 8 ;:
Oil Temperature210F - - -
Cycle Time30 seconds
Reaction Surfaces - Ground and Deburred Soft Steel
Shift 3R ----- lF 3R ~ - 3F
Input RPM 2,000 1,800 1,800 2,000
Coefficient_of Friction
Maximum 0.110 0.110 0.116 0.112 -
Minimum 0.065 o.o68 0.074 0.070
l~lring-In 0.073 0.075 o.o83 o o83
-15-
1C9~L5~)6~
Clutch Tor~ue lb-~t. ~ in2
Max. Dynamic 11.2 11.7 13.3 12.6
W~ing-In 12.6 13.0 14.g 14.9
Peak HP/in2 3.2 2.7 1.7 1.9
Total sTu/in 0.65 0.51 0.48 0.73
Plate Temperature
Max~ F 494 443 360 3Y0
- Bulk F 235 225 212 lY3
The above-described improved friction material is
specifically intended for use in an oil-cooled dlsc-type
friction coupling utilized in a power train such as a clut¢h
or transmission brake for relatively heavy earthmoving
vehicles as depicted in FIG. 8. The representative trans-
mission clutch includes a fluid type housing 20 through
which is journaled a rotatable shaft 22. The shaft has an
integral annular flange 24 which supports a radially out- ,
wardly disposed annular splined ring 25. The ring has a
plurality of axially oriented splines 26 and a plurality
of oil directing openings 28 extended there-through between
the splines. An oil directing and piston receiving chamber
30 is formed between the ring 25, the flange 24 and the
adjacent portion of the shaft 22. A centrally disposed
axially extended bore 32 is formed in the shaft 22 and is
connected to a source of cooling and hydrodynamic braking
fluid, not shown. A port 34 is formed in the shaft 22
between the bore 32 and the chamber 30 for directing the ;
supply of fluid ~oward the plurality of openings 28 in
thR ring 25.
A stationary ring 35 is rigidly mounted within
the housing 20 in radially spaced circumscribing relation
to the ring 25. The ring has a plurality of inner splines 37
~etween whlch are disposed a plurality of fluid exhaust
openings 38. An annular
-16
SV~5
actuating piston IJo is axially slidably mounted ~Jithin the
chamber 30 and has a rad:lally out~lardly extended annular
actuating shoe 42 disposed between the inner and outer rings
25 and 35, respectively. A high pressure rluid passage 45 ls
rormed within the shaft 22 in axially spaced relation to the
bore 32 and is connected to a source o~ high pressure rluid, not
shown. A radially out~.rardly extended passage 46 in the shart 22
communicates such high pressure fluid to a piston actuatlng
chamber 48 in the housing behind the ac~uating piston 40.
A plurality of externally toothed reaction plates 50
are mounted in meshing engagement within the outer ring 35 on
the splines 37 in predetermined axially spaced relation. The
.;. ~ .
reaction plates present opposite substantially flat, smooth
sur~aces 52 with the plates bein~ constructed Or a substantially
rigid noncompressive metallic material. A plurality of intern-
ally toothed ~riction plates 55 are mounted on the splines of ;
.::
the inner ring 25 in interleaved relation to the reaction plates
and in slightly spaced relation thereto. Each of the friction 1 ~
plates has a metallic core 56 and on each of its opposite sides -
has bonded thereto the improved rriction material 57 utilized in
the present invention.
,;,:
As best shown in FIG. 7, such improved ~riction material ,~
is constructed of a composition providing a rluoroelastomer
matrix 58 having a plurality of particles 59 Or a vitreous mater-
ial intermixed therewith and unifo~mly distributed throughout the
matrix in nonbonded relation. Such particles rorm a great multi-
tude of protuberances 60 in the surface of the friction
plate for forming a hy~rodynamic film of oil be-tween each `~
set of ~lates as will subsequently be more ~ully described.
'' "'
3l~4S~65
During operation of the transmission, a continuous
supply of cooling and hydrodynamic braking fluid is directed
through the openings 28 in the inner rotary ring 25, between
each of the interleaved friction plates 55 and reaction
plates 50 and outwardly through the discharge openings 38
in the outer stationary ring 35. Upon the introduction
of high pressure fluid into the actuating chamber 48, the
piston 40 is positioned to the right as shown by the dashed
lines in FIG. 8 which causes the shoe 42 to engage the
stack of friction and reaction plates to initiate the
plate engagement cycle and ultimately compl`ete braking of
the rotary shaft 22. Prior to actual engagement of the
protuberances 60 in the surface of each of the friction ;;
plates with their mating reaction plate, each particle 59
acts as a tiny hydrodynamic bearing. The relatively soft
matrix which serves as a carLier for the partic~es affords
the dual fun~tion of allowing some deflection or partial
recession of the more prominently extended particles into
the matrix itself. In harder matrix materials, the hard
particles would be destroyed as a result of excessive
pressure and possibly torn from the matrix carrier.
Secondly, the relatively soft matrix affords improved ~-
conformability with any irregularities in the mating surface
o~ the reaction plate and permits a more uniform distribution
of pressure ovel substantially the entire area of the
friction plate.
As previously described, the great number of micro-
scopic protuberances 60 in the friction surface of the
friction plate 55 produce a relatively thin film of fluid ,
between them and the mating surface of the reaction plate
through the hydrodynamic wedging of oil on the leading sides
- -18-
. :
~4S~65
of the particles and the cavitation on their trailing sides
as shown in FIG. 7. With the oil film thickness rapidly
approaching that permitted by the microscopic particle size
relatively early during the engagement cycle, the relatively
high rotational speed between the friction plates and reaction
plates produce a relatively high shear rate and torque
absorption in such relatively thin oil film which is sufficient
fully to support the load or pressure of engagement. This
is indicated by the graph of FIG. 6 with the declining portion
of the curve indicating no contact between the surface of the
matrix and the surface of the reaction plate. In direct
contrast, it will be noted that the force curve as shown -~
in FIG. 5 with conventional friction materials indicates --
that the entire load is picked up primarily by the intimate
contact of the surfaces of the plates which continues until
complete wring-in and expulsion of substantially all of the
cooling fluid is achieved. However, with respect to FIG. 6,
as the speed falls, oil shear rate reduces together with `
friction and torque until finally near the end of the engage-
ment cycle the hydrodynamics can no longer be sustained by
the particles due to the low speed and the unit goes into
boundry lubrication, or wring-in, completing the engagement
cycle. It is further noted, however, from the graph of
FIG. 6, that the relative speed is ~ery low when such boundry
lubrication or wring-in occurs, delaying until the last
poss-ible moment any intimate contact of the matrix material `~
with the mating reaction plate, nearly eliminating any load
absorption by the matrix material alone. Accordingly, this
produces a greater resistance to wear of the friction material
and improved temperature stability with a higher coefficient
of friction than heretofore achieved with conventional friction
materials.
--19--
.,, ~
50~S
SUPPLEMENTARY DISCLOSURE
The preferred ranges given in the principal disclosure
for the vitreous or ceramic particles, ~luoroelastomer and carbon
black are 20 to about 50% by weight of vitreous or ceramic par-
ticles, 30 to about 50% by weight of fluoroelastomer and 12 to
about 30% by weight of carbon black. Although these ranges result
in extremely useful compositions, it has been found advantageous
to reduce the lower preferred limit of the amount of fluoroelasto-
mer because this material tends to be the most expensive component
of the composition. Naturally, the maximum preferred amount of
vitreous or ceramic particles and/or carbon black is increased to
compensate for the decreased minimum amount of fluoroelastomer and
it has therefore been found that preferred compositions can be
prepared from the components in the following proportions:
20 to about 60% by weight of vitreous or ceramic particles;
20 to about 50% by weight of fluoroelastomers; and
12 to about 40% by weight o~ carbon black.
In particular, friction materials containing 27%,
25% and 20.5% by weight of fluoroelastomer have been formulated
and these compositions had good structural and rictional
properties.
It has also been found that the fluoroelastomer may
be replaced in part by a polyacrylate matrix material, in
which case the preferred range of the components is 20 to
about 60~ by weight of vitreous or ceramic particles, 20 to about
60% by weight of fluoroelastomer-polyacrylate and 12 to about 40~ ;
by weight of carbon black.
The polyacrylates useful in this 'nvention as part
of the matrix material are ther~osetting elastomers of acrylic
acld and its esters havlng a repeattng structural formula
-CH2 ~ CH (CnOR) - where R ls hydrogen or a low molecular
,~`
.
. .
~45~5
weight alkyl g~oup having one ~o six carbon atoms, e.g., methyl,
ethyl, or one of the propyl, butyl, pentyl, or hexyl isomers.
Generally, the ethyl, propyl and butyl esters are preferred.
Mixed polyacrylates, i.e., those where some of the R groups are
different than others, e.g., some are ethyl and some are butyl
are quite usable. Polyacrylates wherein R is ethyl and also
wherein some R is ethyl and some R is butyl have very desirable
properties. The monomers generally polymerize easily in the
presence of heat, light or catalysts, e.g., benzoyl peroxide
or the like. The inclusion of acrylic anhydride, glycol esters
or acrylic or methacrylic acid or acrylamide is advantageous
in assuring that the resulting resin is insoluble and thermo-
setting. The presence of some acrylonitrile may also be
desirable to adjust resiliency.
Generally, the matrix will include fluoroelastomer
and polyacrylate in weight ratio from about 1:11 to about 11:1.
The preferred weight ratio will fall within the range from
about 1:5 to about 5:1. Further, such matrix will generally
include at least about 5 weight per cent (of the 20-60 weight
per cent total matrix) of fluoroelastomer. Thus, matrices
having from about 5 weight percent fluoroelastomer and about
55 weight percent polyacrylate to matrices having from about
55 weight percent fluoroelastomer to about 5 weight percent
polyacrylate are contemplated as falling within the scope of
the invention.
Generally, the frlction material oE the invention can
be formed by high shear blending together of the solid particles
of the f luoroelastomer component having its appropriate
accelerators, stabilizers and curing agents previously dispersed
therethroughout with solid particles of the polyacrylate
component having its appropriate accelerators, stabilizers and
- 21 - ;
's~
; ~
1~)4S~5
curing agents previously dispersed therethroughout to form a ho-
mogeneous uniForm intimate codispersion of the fluoroelastomer
and the polyacrylate components. The carbon black, vitreous or
ceramic particles and CaO components can be either previously
blended with each of the fluoroelastomer component and the poly-
acrylate component or can be added during the step of blending to-
gether the fluoroelastomer with the polyacrylate. Usually at
least the carbon black will be previously dispersed throughout
both of the fluoroelastomer and polyacrylate components since each
of these components are commercially available in such a form.
It should be noted that the accelerators, stabilizers
and curing agents of the fluoroelastomer are generally different
than the accelerators, stabilizers and curing agents of the
polyacrylate. Thus it is rather surprising that a composite
friction material using a mixture of these two components is
sufficiently structurally sound to exhibit good frictional
and structural characteristics under heavy frictional usage.
Because of the considerably different accelerators, stabilizers
and curing agents generally used with the fluoroelastomer and
polyacrylate components it is believed that at most a minor
amount of cross-lin~ing occurs between the two polymer systems.
Yet, the resulting friction material has both good frictional
and structural characteristics as previously mentioned. The
friction material further exhibits a good thermal operating
range although containing significant amounts of the non-
halogenated polyacrylate component.
The fluoroelastomer-polyacrylate elastomer matrix
has the distinct advantage of being reboundably deflecting at
normal use temperature, as for example when in use as part of
a clutch plate. Normal use temperature, as discussed previously
include average sur~ace temperatllres between operations of
. : ,
1.()45(~6S
generally helow nl~out 4751~. (;en~rally, norm.ll usc tcmpera-
tures will bc a~ least about 180 F in frictional operation.
Thus, the matri~ ls reboundably deflecting and resillent ln
the temperature range from about 180 F to about ~75 F. The
term reboundably deflectlng as used herein means that the
vitreous or ceramic particles which are at the surface of the
material are pushed or deflected thereinto during contact with a
mating reaction plate as in a clutch but then rebound back as the
material resumes its natural or unstressed state when the mating
lO reaction plate is removed from contact therewith. It is ,,
clearly of great advantage to have a frlctlon materlal that is
reboundably deflecting at its use temperature yet is not easily
or quickly worn away (due to the vitreous or ceramic particles)
since this allows for a controlled and relatively smooth change
in friction as pressure is applied between the material and a
mating reaction plate plus long wearing characteristics. '~
Description of the_~dditional Drawin~ -
Figure 9 illustrates ln greatly enlarged view a
section through the improved friction material disposed adjacent
a substantially flat reactlon plate with a relatlvely thin
energy absorbing o~l film therebetween and with a metal backlng
plate bonded thereto.
Figure 10 illustrates in greatly enlarged view the sur-
face of the improved friction material after this surface has
been "worn in". The vitreous or ceramic are noted to have flat-
tened upper surfaces produced upon "wearing in" of the material.
The structure and operatlon of the friction material
may be still better understood by reference to the flgures of
the ~dditional Drawings wherein like numbers denote like parts
throughout. A friction material 10 in accordance with the
present inventlon is illustrated as including a matrix 12 of
, ~ .
- 23 -
', . , , , ' ' ' ' , ~, , ` , ' . :
5~tj5
previously mentioned composition with vitreous or ceramic
particles 14 suspended mechanically therein in non-bonded
relationship thereto. The friction material 10 is bonded to a
metal backing plate 16. In operation, the surface of the friction
material 10 removed from the backing plate 16 faces a ~ating plate
18 with a fluid layer 20 generally therebetween. In operation in
a clutch, the mating plate 18 and the facing surface of the
friction material 10 are forced towards one another while rotating
relative to one another. Thus, a high shear is introduced in the
fluid layer 20 whereby a substantial amount of the energy of clutch
engagement is absorbed. On contact, a top portion 22 of each
protruding one of the particles 14 touches the mating plate
18 and the particles 14 thus tend to flatten as illustrated in
Figure lO. ~lso, due to the reboundably deflecting character
of the matrix 12 at use temperature the protruding particles 14
are puslled down against the matrix 12. On release of pressure,
as when the mating plate 18 is moved away from the frictlon
material 10, the particles 14 spring up under the impetus of
the resilient matrix 12 and return generally to their original
protuberance above said matrix ~2. ~hus, relatively smooth
clutch engagement occurs, first via the fluid 20 shear, then
via particles 14 during their partial retraction into the
matrix 12 and finally via the direct supported contact of the
particles 14 with the mating plate 18.
The following additional Example is provided only
to further illustrate specific friction material compositions
and pertinent frictional characteristics thereof, without
limiting the invention in any manner:
- 24 -
- .,, ':
. .
~L~45~;S
~dditional l~xample
Ingredients A~
Formula I Formula II
Viton R60 50 Parts 70 Parts
Polyacrylate 50 Parts 30 Parts
Fiberfrax 30 Parts 110 Parts
Carbon Black 50 Parts 57 Parts
Accelerators )
Stabilizers ) Minor amounts Minor amounts
10 Curing Agents)
CaO 5 Parts 5 Parts
The clutch plate having Formula I affixed thereto
exhibited dynamic coefficients of friction of 0.114 at 7000 fpm
(feet per minute) and 50 psi, 0.086 at 5000 fpm and 25Q psi and
0.071 at 7000 fpm and 250 psi. The failure point of this
clutch plate was above 11,000 fpm. The wear of the friction
material on this plate at 7000 fpm and 250 psi was 1 mil. Wear -
was measured by a screening test comprising 120 to 2pO cycles -
of break in at 5000 fpm and 100 psi.(until the dynamic co-
efficient of friction stabilized) followed by a cycle of 15
clutch engagem~ents each at 50 psi, 150 psi and 250 psi at 3000
fpm, then a cycle of 15 clutch engagements each at 50 psi, 150
.. ..
psi and 250 psi at 5000 fpm, and then a cycle of 15 clutch
engagements each at 50 psi, 100 psi, 150 psi, 200 psi and 250
psi at 7000 fpm. The clutch was perlodically checked at 5000
fpm and 100 psi to assure that no significant change in dynamic
coefficient of friction had occured. Wear values obtained were
generally good to about ~ 0.3 mil.
The clutch plate having Formula II affixed thereto
exhibited dynamic coefficients of friction of 0.089 at 7000 fpm
and 50 psi, 0.088 at 5000 fpm and 250 psi and 0.081 at 7000 fpm
- 25 -
. . .
~'~
~s~s : ~
-- and 250 ~si. l`lle failure point of Ll~is clutcll pl.ntc w~s not
measllre(l. l`ho rate o~ wear of the friction material on this
plate at 7000 fpm and 250 psi was 0 mil.
In each case the Formulas were compounded by mixing
in a Banbury mixer to achieve an even dispersion of the
additives into the matrix and of the two components (the
fluoroelastomer and tlle polyacrylate) of the matrix into one
anotller with random orientation of the (Fiberfrax) ~-
particles.
Each Formula mixture was applied to a steel backing
plate and pressed to this plate into the desired pattern under
about 2,500 psi. Formula I then was cured for 30 minutes at -
335 - 340 F and Formula II for 10 minutes in the same tem-
perature range. Sufficient mixture material was applied to
each plate to give a thickness of material, when cured, of
.050 inches/face. The cured elastomer and backing plate, i.e.,
clutch disc, were then postcured at 450 F for 3 hours.
The friction material possessed a Shore A Hardness
of 90 - 95, and an ultimate tensile strength of 1,900 to 2,100
psi. The friction material was foun~ to have an e~cellent
thermal stability.
While the invention has been described in connection -
with speclfic embodiments thereof, it will be understood that
it is capable of further modification, and tllis application is
intended tc cover any variations, uses or adaptations of the
invention following, in general, the principles of the invention
and including such departures from the present disclosure as
come within known or customary practice in the art to which the
invention pertains and as may be applied to the essential
features herelrlbefore set forth, and as fall within thc scope
of the invention and the ~imlts of the appended clalms.
- 26 -
.
