CA1045065A - Friction coupling - Google Patents
Friction couplingInfo
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- CA1045065A CA1045065A CA232,633A CA232633A CA1045065A CA 1045065 A CA1045065 A CA 1045065A CA 232633 A CA232633 A CA 232633A CA 1045065 A CA1045065 A CA 1045065A
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Abstract
FRICTION COUPLING
Abstract of the Disclosure A friction coupling which utilizes a friction plate composed of high modulus vitreous or ceramic parricles incorporated into a reboundably compressible elastomeric matrix for selective rotational engagement with a relatively noncompressible reaction plate between which is directed a flow of fluid with the high modulus particles hydrodynamically wedging such fluid into a relatively thin load supporting film between the particles and the reaction plate which film absorbs substantially all of the energy of engagement in the shearing effect of the fluid during relative rotation of the plates.
Abstract of the Disclosure A friction coupling which utilizes a friction plate composed of high modulus vitreous or ceramic parricles incorporated into a reboundably compressible elastomeric matrix for selective rotational engagement with a relatively noncompressible reaction plate between which is directed a flow of fluid with the high modulus particles hydrodynamically wedging such fluid into a relatively thin load supporting film between the particles and the reaction plate which film absorbs substantially all of the energy of engagement in the shearing effect of the fluid during relative rotation of the plates.
Description
~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,
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,
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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 ~
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-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 ... . . . . ..
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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 .
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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.
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~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.
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~ ' ~'''.'. "' 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. ;
~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.
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- 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.
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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 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 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 ;
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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 . :
~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.
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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 , ~ .
', . , , , ' ' ' ' , ~, , ` , ' . :
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:
- .,, ':
. .
~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 . . .
~'~
~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.
.
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 .
' ~=-;,. :
.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. ;
~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.
.
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 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 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 . :
~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.
.,, ~
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 , ~ .
', . , , , ' ' ' ' , ~, , ` , ' . :
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:
- .,, ':
. .
~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 . . .
~'~
~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.
.
Claims (18)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. 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 of elastomeric materials consisting of polyacrylate, silicone, fluorosilicone, chloro-prene, acrylonitrile, urethane, and hexafluoropropylene-vinylidene fluoride copolymer 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 intermixed 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 maximum conformability to said mating surface 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 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 substan-tially all of the energy of plate engagement to be absorbed in shear of said fluid film until just prior to complete engagement of the plates.
a rotatable friction plate formed of a matrix of a relatively soft elastomeric material providing a friction surface and selected from the group of elastomeric materials consisting of polyacrylate, silicone, fluorosilicone, chloro-prene, acrylonitrile, urethane, and hexafluoropropylene-vinylidene fluoride copolymer 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 intermixed 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 maximum conformability to said mating surface 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 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 substan-tially all of the energy of plate engagement to be absorbed in shear of said fluid film until just prior to complete engagement of the plates.
2. A friction coupling as in claim 1, in which said elastomeric material comprises a copolymer of hexafluoropropylene and vinylidene fluoride.
3. A friction coupling as in claim 1, in which said elastomeric material comprises polyacrylate.
4. A friction coupling as in claim 1, in which said elastomeric material comprises silicone.
5. A friction coupling as in claim 1, in which said elastomeric material comprises fluorosilicone.
6. A friction coupling as in claim 1, in which said elastomeric material comprises chloroprene.
7. A friction coupling as in claim 1, in which said elastomeric material comprises acrylonitrile.
8. A friction coupling as in claim 1 in which said elastomeric material comprises urethane.
9. A friction coupling comprising:
a rotatable friction plate formed of a matrix of a relatively soft elastomeric material providing a friction surface;
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 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 fluid provided between said plates with the fluid during movement of the plates toward each other hydrodynamically 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 particles into the matrix for permitting complete engagement of the entire surface areas of the plates.
CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
a rotatable friction plate formed of a matrix of a relatively soft elastomeric material providing a friction surface;
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 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 fluid provided between said plates with the fluid during movement of the plates toward each other hydrodynamically 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 particles into the matrix for permitting complete engagement of the entire surface areas of the plates.
CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE
10. The friction coupling of claim 1 wherein the elastomeric matrix comprises from about 20 to about 50% by weight of a fluoroelastomer matrix material, from about 12 to about 40% by weight of carbon black, and from about 20 to about 60% by weight of particles of a vitreous or ceramic material.
11. The friction coupling of claim 10 wherein the particles have an effective diameter of from about 0.0001 to 0.005 inches and the particles are intermixed with and dispersed through the matrix material in mechanically held non-bonding relation to provide a friction surface on said matrix which includes said particles which form said protuberance means.
12. The friction coupling of claim 10 wherein the particles are glass fibers of a size from about 0.0001 to about 0.005 inches in diameter and having a length to diameter ratio of from about 3 to 10,000.
13. The friction coupling of claim 1 wherein the elastomeric matrix comprises a fluoroelastomer intimately intermixed with a polyacrylate elastomer.
14. The friction coupling of claim 1 wherein the elastomeric matrix comprises a friction material formed of 20% to 60% by weight of a matrix comprising a fluoroelastomer intimately intermixed with a polyacrylate elastomer in a weight ratio of fluoroelastomer to polyacrylate which falls within the range from about 11:1 to about 1:11, at least 5% by weight of said 20% to 60% by weight total matrix being said fluoro-elastomer, from about 12 to about 40% by weight of carbon black; and from about 20% to about 60% by weight of ceramic or vitreous particles of from about .0001" to about .005" in effective diameter intermixed with and dispersed throughout said friction material in mechanically held nonbonded relation to provide said friction surface having protuberance means formed by said particles.
15. The friction coupling of claim 14, wherein said fluoroelastomer comprises a copolymer of hexafluoropropylene and vinylidene fluoride and said polyacrylate elastomer has a repeating structural formula - CH2 - CH (COOR) - where R is hydrogen or a low molecular weight alkyl group having one to six carbon atoms.
16. A friction material as in claim 15, wherein the weight ratio of fluoroelastomer to polyacrylate falls within the range from about 5:1 to about 1:5.
17. The friction coupling of claim 1 wherein the elastomeric matrix comprises 20% to 60% by weight of a matrix consisting essentially of a copolymer of hexafluoro-propylene and vinylidene fluoride intimately intermixed with a polyacrylate elastomer in a weight ratio of fluoroelastomer to polyacrylate which falls within the range from about 11:1 to about 1:11, at least 5% by weight of said 20% to 60% by weight total matrix being said fluoroelastomer, from about 12 to about 40% by weight of carbon black; and from about 20 to about 60% by weight of ceramic particles having a minimum size of .0001" which are dispersed throughout the matrix in mechanically held nonbonded relation and assuring a relatively high surface concentration of the ceramic particles on said friction surface.
18. The friction coupling of claim 17 wherein said ceramic particles are glass fibers of a size from about .0001"
to about .005" in diameter and having a length to diameter ratio of from about 3 to 10,000.
to about .005" in diameter and having a length to diameter ratio of from about 3 to 10,000.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US54414875A | 1975-01-27 | 1975-01-27 | |
| US05/595,822 US4051100A (en) | 1973-06-04 | 1975-07-14 | Fluoroelastomer-based composite material |
| US05/601,398 US4045402A (en) | 1973-06-04 | 1975-08-01 | Fluoroelastomer-polyacrylate based friction material |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1045065A true CA1045065A (en) | 1978-12-26 |
Family
ID=27415425
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA232,633A Expired CA1045065A (en) | 1975-01-27 | 1975-07-31 | Friction coupling |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1045065A (en) |
-
1975
- 1975-07-31 CA CA232,633A patent/CA1045065A/en not_active Expired
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