Improved friction material composition and associated friction element

Abstract

An asbestos free friction material composition and associated brake pad for vehicles, in particular for electric vehicles, including at least one filler, at least inorganic and / or organic fibers, at least one organic binder, at least one lubricant and at least one mild abrasive and at least one hard abrasive, wherein further including a thermally conductive, non-roundish, metallic powder substantially free of copper and / or of any metallic alloy including copper; and wherein the ratio in %vol between the content of hard abrasive and lubricant is between 0.1 and 1.5.

Description

[0001] " IMPROVED FRICTION MATERIAL COMPOSITION AND ASSOCIATED

[0002] FRICTION ELEMENT"

[0003] Cross-Reference to Related Applications

[0004] This Patent Appl ication claims priority from Italian Patent Application No . 102024000023061 filed on October 16 , 2024 , the entire disclosure of which is incorporated herein by reference .

[0005] Technical Field

[0006] The present invention relates to a friction material composition particularly suitable for the manufacture of friction layers / blocks for friction elements such as braking elements to be incorporated in a vehicle braking system .

[0007] The invention also relates to an associated fiction element , for example brake pads or brake shoes for vehicles , made with this friction material composition and particularly but not exclusively suitable for electric vehicle .

[0008] The friction material composition of the present invention is free of asbestos and substantially free of copper, and consi sts in a hybrid material , developed on the basis of so-called NAO ("Non Asbestos Organic" ) formulations to meet requirements of single layer coated rotors . Its main characteristics are related to stability of the friction level , the ability to pass high stressing test as AMS and HFT and to generate very low level s of dust particles during WLTP test .

[0009] State of the Art

[0010] With the rapid development of modern transportation industry, the number o f electric vehicles is increasing day by day . The replacement of combustion engine with an electrical one leads to much more silent vehicles. This is bearing higher attention to those noises generated by other car components, such as by the brake pad used in the braking system. Consequently, the brake pad used for electrical vehicles requires improved NVH (Noise, Vibration, Harshness) criterion for driving comfort.

[0011] Likewise, maximum attention is to be given in generating low emissions, not only regarding combustion (which does not exist in electric vehicles) but above all relating to micro-particulates that can be released during braking .

[0012] Copper, when used in a friction material composition designed to produce brake elements, may be useful but, unfortunately, is seen nowadays as a polluting material, so its use should be avoided.

[0013] As mentioned, the advent of vehicle electrification brings the silence of the vehicles to be a goal of paramount importance and requires the use of friction materials developed to obtain in use a tribological mechanisms such as the generation of low frequency noise is not produced. The tribological mechanisms that induces low frequency noise is known and is referred to as the "stick-slip" phenomenon .

[0014] In particular, the stick-slip phenomenon may bring to the generation of the so called "Creep groan" low frequency noise, especially at very low speeds of the vehicle. It is the classic example of a self-excited braking vibration by alternated episodes of sticking or adhesion and subsequent slipping of the brake pad on the brake disc during the braking process and, as a result, the coefficient of friction continuously varies between a static (stick phase) and dynamic (slip phase) values.

[0015] Various solutions are known in the art, e.g. from EP0959262, to try to reduce this phenomenon, but they either do not solve completely the problem or present additional drawbacks, as high cost and complex accomplishment.

[0016] To reduce the particulate emission, a solution may be to use the so-called single layer disc rotors as a friction partner of a brake pad. The single layer disc rotors consist in "normal" cast iron (generally grey cast iron) brake discs, having the braking surfaces thereof covered with a single layer coating consisting of an alloy of Fe, Ni and / or Cr, e.g., an Ni-Cr stainless steel.

[0017] However, the "normal" NAO friction material commonly used, when coupled with such a kind of single layer disc rotors show a low stability of the friction coefficient and a relatively high level of noise due to the roughness of the single layer disc rotors. Friction materials like those described in EP2882977B1 of the same Applicant, may be too aggressive with the braking surfaces of the disc rotors, causing e.g., scratches, which further increase the level of noisiness .

[0018] Summary of the Invention

[0019] The object of the present invention is to develop a new asbestos free friction material composition, which can overcome the disadvantages of the prior art . In particular, the presently disclosed subject matter is intended to provide an asbestos free friction material composition, specifically studied for use in conjunction with single layer brake discs, which substantially reduces the tendency of the friction block to stick against a surface of the friction partner cooperating therewith, like a single layer brake disc, so reducing noise and keeping almost constant the coefficient of friction, and, at the same time, reduces to a minimum the amount of micro-particulates released during braking.

[0020] The invention is therefore related to a friction material composition as defined in the appended claims.

[0021] It is a further object of the invention to provide a friction element, in particular a brake pad or brake shoe, including this friction material composition.

[0022] Finally, it is a further object of the invention to provide a braking system including a brake pad and a disc rotor cooperating thereto having a reduced release of microparticulate during braking, an almost constant friction coefficient and a reduced noise and tendency to be subject to the stick-slip phenomenon.

[0023] The present disclosure demonstrates how, starting from any known friction material formulation of the well-known NAO type (see e.g., Kim, Seong-Jin et al., Study of Friction Characteristics of Non-asbestos Organic (NAO) and Semimetallic Brake Pads During Automotive Braking, Tribology and Lubricants, Volume 13 Issue 3, Pages.10-19, 1997, 2713- 8011 (pISSN) / 2713-802X (elSSN) ) , the addition of an appropriate quantity of non-roundish metallic powder, preferably iron-based metallic powder with specific heat transfer characteristics, in combination with a carefully selected ratio between hard abrasives and lubricants and substantially eliminating copper, not only may meet the most stringent US copper regulation but also, and above all, allows to mitigate the stick-slip phenomenon, to obtain a substantially constant friction coefficient and to substantially reduce , well below the limits established by the law, the release of micro-particulates during braking .

[0024] In particular, the quantity of hard abrasives has been reduced in comparison with their quantity normally contained in a standard NAO friction material and, above all , an hard abrasive which is commonly present in NAO formulations , namely Zirconium oxide , has been removed or its amount in the friction material has been strongly reduced, at least below 5% by volume calculated on the total volume of hard abrasives present in the innovative friction material of the present invention .

[0025] Further features and advantages of the disclosed subj ect matter, whether explicitly mentioned or not , will become apparent in view of the disclosure provided below .

[0026] This disclosure therefore relates to a friction material composition, substantially derived from the class of friction materials known as NAO (Non Asbestos Organic ) , which aims to obtain an improved stick-slip behavior for the benefit of the creep groan phenomenon and friction stability, with respect to known NAO friction compositions and, above all , for the benefit of strongly reducing the release of micro-particulates in the environment during braking action .

[0027] Brief Description of the Drawings

[0028] Further characteristics and advantages of the present invention will become clear from the following description, from practical and comparative non-limiting examples and with reference to the attached drawings , in which :

[0029] - Figure 1 shows schematically only a three-quarter perspective view from one side of a braking system made according to the present invention;

[0030] - Figure 2 shows a SEM micrography of a component of the friction material composition according to the invention;

[0031] - Figure 3 shows a diagram obtained by laser scattering illustrating the granulometric distribution of the component of figure 2 ;

[0032] - Figure 4 shows graphs illustrating for comparative purposes a first most signi ficative part of the result of a standard AK-Master test modi fied for electric vehicle (EV) carried out on a friction element made of a NAO friction material composition according to the prior art ;

[0033] - Figure 5 shows graphs illustrating the same first most signi ficative part of figure 4 of the result of the same standard AK-Master test modi fied for electric vehicle (EV) carried out on an identical friction element but made of a NAO friction material composition according to the invention;

[0034] - Figure 6 shows graphs illustrating for comparative purposes a second most signi ficative part of the result of a standard AK-Master test modi fied for electric vehicle (EV) carried out on a friction element made of a NAO friction material composition according to the prior art ;

[0035] - figure 7 shows graphs illustrating the same second most signi ficative part of figure 6 of the result of the same standard AK-Master test modi fied for electric vehicle (EV) carried out on the identical friction element but made of a NAO friction material composition according to the invention;

[0036] - Figure 8 shows graphs illustrating for comparative purposes a third most signi ficative part of the result of a standard AK-Master test modi fied for electric vehicle (EV) carried out on a friction element made of a NAO friction material composition according to the prior art ;

[0037] - figure 9 shows graphs illustrating the same third most signi ficative part of figure 8 of the result of the same standard AK-Master test modi fied for electric vehicle (EV) carried out on the identical friction element but made of a NAO friction material composition according to the invention;

[0038] - Figure 10 shows a graph illustrating the results of a FADE test carried out on a friction element made of a NAO friction material composition according to the prior art ;

[0039] - Figure 11 shows a graph illustrating the results of the same FADE test carried out on the same friction element but made of a NAO friction material composition according to the invention; and

[0040] Figure 12 shows comparative bar diagrams of the extrapolated results of a WLTP standard test carried out on a brake pad made with a standard NAO friction material and on an identical brake pad made with the friction material of the invention coupled with a single coated brake di sc rotor according to the braking system of the invention .

[0041] Detailed Description

[0042] In more detail , the disclosed asbestos free friction material composition comprises at least one filler, at least a fibrous material , at least one binder , at least one lubricant , at least one or more abrasives and a non- negligible quantity of a thermally conductive , non-roundish, metallic powder substantially free of copper and / or of any metallic alloy including copper .

[0043] Here and in the following, for " substantially free" of copper or its alloys is to be intended a content of copper or its alloys below 0 . 5% by weight . The thermally conductive , non-roundish, metallic powder is an iron-based metallic powder, preferably selected from the group consisting of iron, an iron alloy, steel , stainless steel , any combination thereof and is contained in the friction material composition in a quantity in volume comprised between 2 %vol and 10%vol .

[0044] The thermally conductive , non-roundish, metallic powder has a speci fic surface area of about 200-220 m2 / kg and a granulometric profile (particle si ze distribution) comprising :

[0045] • a Dvio about 10-20 ,

[0046] • a Dvso about 30-50

[0047] • a Dvgo about 57- 60 .

[0048] Here and in the following, "particle si ze distribution D50" corresponds to the value of the particle larger dimension at 50% in the cumulative distribution . Likewise , Dio corresponds to the value of the particle larger dimension at 10% in the cumulative distribution and D90 corresponds to the value of the particle larger dimension at 90% in the cumulative distribution .

[0049] According to an aspect of the invention, in combination with the presence of the thermally conductive , non-roundish, metallic powder, the at least one or more abrasives include at least a mild abrasive having a Mosh hardness lower than 7 and at least a hard abrasive having a Mosh hardness higher than 7 , and the ratio between the content in %vol of hard abrasives and the content in %vol of lubricants is to be comprised between about 0 . 1 and 1 . 5 .

[0050] In preferred embodiments , the ratio between the content in %vol of hard abrasives having a Mosh hardness >7 and the content in %vol of lubricants is comprised between about 0 . 16 and 0 . 36 .

[0051] The other components of the disclosed friction material composition, above mentioned, may be components used in frictional materials already known in the art .

[0052] In particular, the at least one fibrous material can be selected from the group consisting of inorganic fibers , organic fibers , and any combination thereof .

[0053] Preferably, the at least one fibrous material consists in organic fibers selected from the group consisting of polyacrylic fibers , polyaramid fibers , aramid fibers , cellulose fibers and mixtures thereof .

[0054] The organic fibers may be, preferably but not exclusively, contained in the friction material composition of the present disclosure as a part of the organic binder, since they may have the main obj ect to increase the strength thereof under the operative working conditions of the brake pads / shoes which may be manufactured from the friction material composition of the present disclosure .

[0055] The at least one binder is preferably an organic binder and may be selected from the group consisting of phenolic resins , epoxy resins , siliconic resins , modi fied phenolic resins , melamminic resins , polymmide resins and mixtures thereof .

[0056] The at least one lubricant may consist , preferably but not exclusively, of a sulphide-based lubricant selected from the group consisting in metal sul fides of Sn, Zn, Fe , Mo , and mixtures thereof .

[0057] Numerous materials may be used as organic or inorganic fillers . Inorganic fillers may be selected from the group consisting of : barite , mineral fibers , glass fiber, rockwood, phillosilicates other than vermiculite (e.g. mica, talc, etc.) , inorganic hydroxides of Calcium, Magnesium, Potassium, and any mixture thereof.

[0058] The at least one or more abrasives must comprise, according to an aspect of the inventio, at least one soft abrasive having a Mohs hardness of below 7 and at least one hard abrasive having a Mohs hardness of above 7.

[0059] The ratio between the content in volume of the soft abrasive and of the hard abrasive is ranging from 4:1 to 35:1 and may be preferably 16:1.

[0060] Hard abrasives (i.e. having a Mohs hardness of above 7) may be selected, preferably but not exclusively, in the group consisting of alumina, corundum, silicon carbide, tungsten carbide, zirconium carbide, zirconium silicate, boron nitride and any mixture thereof.

[0061] According to a feature of the invention, the friction material composition has a substantially zero or reduced content in the hard abrasive consisting of zirconium oxide. In fact, the maximum %vol allowed of zirconium oxide, calculated on the total content of hard abrasives being lower than 5%.

[0062] Soft abrasive (i.e. having a Mohs hardness of below 7) may be selected, preferably but not exclusively, in the group consisting of magnesia, chromite, magnetite, hematite, quartz, zinc oxides, tin oxides, barium sulphate, silicate, fluoride and any mixture thereof.

[0063] In addition, the disclosed friction material composition may comprise organic additives including hydrophobic agents like PTFE or a wax, damping agents like rubber particles, friction dust; the organic additives may therefore be selected from the group consisting of polytetrafluoroethylene , friction dust , cashew dust , rubbers other than silicon rubber, e . g . NBR, SBR, etc .

[0064] The disclosed friction material composition may comprise also graphite and / or coke .

[0065] In further embodiments of the present invention, the friction material composition may be as follows ( % is in volume ) :

[0066] Abrasives Mohs >7 2- 8

[0067] Abrasives Mohs <7 30-70

[0068] Organic Binder (Resin) 6- 10

[0069] Organic additives 3- 8

[0070] Fibers 2- 8

[0071] Lubricants 6- 15

[0072] Metal powder 2- 10

[0073] In preferred embodiments of the invention the ratio between the content of the metallic powder and the content of organic additives is such that the thermal conductivity of the friction material composition is comprised, preferably but not exclusively, between about 0 . 5 and 2 W / m°K, and even more preferably, comprised between 1 . 5 and 1 . 8 W / m°K .

[0074] The invention also relates to a friction element , in particular a brake pad or brake shoe , presenting a layer of friction material made from the friction material composition described above .

[0075] The invention further relates to a braking system comprising a member to be braked, constituted by a brake disc or brake drum made of cast iron or steel and at least one braking element constituted by a brake pad or shoe which is designed to cooperate by means of friction with the member to be braked, wherein the braking member presents a friction layer which is intended to cooperate with the member to be braked and which is made of the friction material composition described above .

[0076] In particular, the braking member is a brake pad including a metal support and a friction layer or block having a thermal conductivity comprised, preferably but not exclusively, between about 0 . 5 and 2 W / m°K and even more preferably, comprised between 1 . 5 and 1 . 8 W / m°K .

[0077] Preferred embodiments of the invention relate to a braking system comprising a member to be braked constituted by a brake disc made of cast iron and at least one braking member constituted by a brake pad, adapted to cooperate by friction with a friction surface o f the brake disc, wherein the brake pad has a friction layer intended to cooperate with the friction surface of the brake disc made of a friction material composition described above and, in combination, the friction surface of the brake disc is coated with a single layer coating of a Fe alloy with Ni and / or Cr .

[0078] In particular, the single layer coating of the friction surface of the cast iron, preferably gray cast iron, brake disc and cooperating with the brake pad consi sts of a stainless-steel alloy .

[0079] Exemplary modes o f carrying out the teaching of the present disclosure

[0080] Inventive and comparative examples are reported herein by way of illustration and are not intended to limit the invention .

[0081] With reference to figure 1 , the reference number 1 indicates a brake disc rotor for vehicles . Brake di sc rotor 1 ( or merely brake disc 1 ) is part of a braking system 2 comprising the brake disc rotor 1 , which is the member of the system 2 to be braked , a caliper 3 mounted astride the brake disc rotor 1 an a pair of braking elements constituted by brake pads 4 carried by the caliper 3 and configured to cooperate in use with opposite friction surfaces 5 of the brake disc 1 under the control of a braking central unit 6 , which activate the caliper 3 when a driver brakes the vehicle , pressing the two brake pads 4 against the friction surfaces 5 in order to dissipate by friction the motion energy of the brake disc 1 , so as to slow down its rotation until the vehicle is stopped .

[0082] According to an aspect of the present invention the brake disc 1 is a so called " single layer brake dis rotor" since both its friction surfaces 5 are coated with a single layer coating 7 .

[0083] According to an aspect of the invention, as it will be explained later, the brake disc 1 is made of cast iron, preferably gray cast iron and the single layer coating 7 is made of a Fe alloy, wherein Fe is alloyed with Ni and / or Cr and possibly other elements .

[0084] In preferred embodiments the single layer coating 7 is made of a stainless steel with a surface hardness comprised between about 300- 900 HV and more preferably 300-700 HV (Vickers degrees ) and a roughness Ra < 1 micron and Rz < 5 micron . As the skilled persons wel l known, Ra is calculated by an algorithm that measures the average length between the peaks and valleys of a real surface and the deviation from the mean line on the entire surface within the sampling length . Ra averages all peaks and valleys of the roughness profile and then neutrali zes the few outlying points so that the extreme points have no signi ficant impact on the result . Rz , on the contrary, is calculated by measuring the vertical distance from the highest peak to the lowest valley within five sampling lengths , then averaging these distances . Rz averages only the five highest peaks and the five deepest valleys , therefore , extremes have a much greater influence on the final value in comparison with Ra .

[0085] Each brake pad 4 comprises a metal support 8 , generally made of iron or steel , but also of a light alloy of Al , and a friction layer 9 carried by the support 8 and intended to cooperate with the friction surface 5 of the brake disc 1 and speci fically with the single layer coating 7 covering the friction surfaces 5 . According to one aspect of the invention, in combination with the presence of the single layer coating 7 covering the friction surfaces 5 , the friction layer 9 is made of a friction material composition according to embodiments of the present invention, prepared as it will be disclosed in the following working examples . Exampl e 1

[0086] Several formulations of a friction material were prepared starting from the backbone of a common NAO friction material .

[0087] The component raw materials of the prepared formulations are shown in Table 1 and are indicated in percentage values by volume of the total volume of the composition .

[0088] TABLE 1

[0089] The metal powder component is shown in the micrography of figure 2 . It consists , according to one feature of the invention, in a thermally conductive , non-roundish, ferrous metal powder substantially free of copper and / or of any metallic alloy including copper and made of irregular particle of any of iron, iron alloy, steel , stainless steel .

[0090] In the present working examples , an iron powder was used having the granulometric profile as shown in figure 3 .

[0091] The components shown in Table 1 were uni formly mixed in a Hori zontal Mixer ( e . g . Loedige kind mixer ) and molded in a mold under a pressure of 20 tons for 3 minutes at a temperature of about 150- 170 ° C, then cured from 10 minutes to 10 hours at temperature ranging from 150 ° C to 400 ° C, producing five series of friction materials blocks .

[0092] A first series , marked in the following as NAO, was produced for comparative purposes and its formulation corresponds to the average values of the intervals of composition given in Table 1 in the first left-hand column marked NAO, which reports the well-known composition interval of standard friction material NAO compositions .

[0093] Three series were prepared with formulations based on random changing the values of composition intervals given in the second, middle column of Table 1 .

[0094] A final fi fth series was prepared with the formulation given in the right-hand column of Table 1 .

[0095] Each block of friction material so obtained was made integral with identical metal supports consisting in flat steel plates (back-plates ) to form vehicle brake pads .

[0096] Exampl e 2 : AK Master Test In order to understand whether or not the addition of ferrous metal powder may af fect the braking performances the batches of brake pads produced in the manner described in Example 1 were subj ected to an ef ficiency test according to the known AKM Master Test , including : settling braking, braking at di f ferent fluid pressures , " cold braking" (<50 ° C ) evaluation, highway simulation braking, two sets of high energy braking ( f irst FADE test ) interspersed with a series of recovery braking . From this test it is also possible to extrapolate , in a way known to those skilled in the art , the general behavior of the fiction material mixture compositions and the coef ficient o f friction during the whole test duration .

[0097] The results obtained, performing the braking using as the member to be braked, several identical single-layer coated gray iron brake disc, are illustrated in Figures from 4 to 11 , which schematically represents an extract of the signi ficant data of the experimental curves obtained according to a standard and well-known AK Master test modi fied for electric vehicles (EV) , as described briefly above .

[0098] Figure 4 shows part of the experimental curves relating to the friction stability, namely the variation of the friction coef ficient during repeated braking, obtained using the reference sample constituted by a standard NAO friction material within the composition intervals of the left-hand column of Table 1 . Figure 5 shown the same part of experimental curves of figure 4 obtained using a sample made according to the right-hand column composition of Table 1 .

[0099] As it is immediately apparent , the curves relating to the friction material of the invention are quite more favorable . Especially referring to the third panel ( righthand column) in the reference sample ( Standard NAO material ) the value of the friction coef ficient goes out of scale , as shown by the arrow . On the contrary, in figure 5 the value of the friction coef ficient is maintained substantially constant .

[0100] Figures 6 and 8 show di f ferent section of the experimental curves for the reference standard NAO sample , while figures 7 and 9 show the same sections of the experimental curves for the modi fied NAO sample prepared with the formulation according to the invention shown in Table 1 . Again, the quire better performances of the latter are evident for the skilled in the art .

[0101] Figures 10 and 11 show the FADE section of the experimental curves .

[0102] As shown in figure 10 , the reference sample made of a standard NAO material presents a friction coef ficient which is quite variable within the interval of interest delimited by two hori zontal lines and which, as shown by the arrow and the relating label , causes an alarm on the dynamometer due to too high torque values .

[0103] As shown in figure 11 , on the contrary, the modi fied NAO sample prepared with the formulation according to the invention shown in Table 1 and tested together with a single layer coated grey cast iron brake disc shows a higher stability, especially within the interval of interest delimited by two hori zontal lines .

[0104] In conclusion, the AK Master test shows a dramatically better result for the samples made with the friction material according to the invention, when coupled to a single layer coated gray cast iron brake disc . Example 3: WLPT Test

[0105] The Worldwide Harmonized Light Vehicle Test Procedure (WLTP) is a globally standardized test procedure for determining the levels of pollutants, CO2 emissions, and fuel consumption of cars. It was initially published by the United Nations Economic Commission for Europe (UNECE) in 2014.

[0106] The Particles Measurement Program (PMP) sponsored by the United Nations Working Party on Pollution and Energy (UNECE-GRPE) promoted the investigation.

[0107] The cycle for braking emission evaluation is based on the EU part of the WLTP database. The cycle aims to reproduce the vehicle test with a dynamometer. The cycle is divided into 10 trips, with an increasing average speed: 303 stops over 192 km and net test duration of 4:24 h. Soaking times are planned between each trip in order to cool down the disc to 40°C before each trip. The complete test is made of 6 WLTP repetition for approx. 40 h of test time.

[0108] The test was carried out using a single layer coated gray cast iron standard brake disc with a stainless still coating using for comparative purposes brake pads having a standard NAO friction layer and identical brake pads having a modified NAO friction layer according to the invention. The results are reported in figure 12 in terms of mg of micro-particulates released per km traveled. The straight dotted line indicates the emission limit established by EU 6 ICE regulations.

[0109] As it can be seen, while the standard NAO friction material (marked GA7504) generates an amount of microparticulate fairly exceeding the EU 6 ICE limit, the modified friction material according to the invention (marked GA5900) remains far below the limit. Exampl e 4 : Conducti vi ty test

[0110] The conductivity of the friction material blocks of the friction elements of the preceding test are subj ected to a standard conductivity test at dif ferent temperatures . The results are reported in Table 2 .

[0111] The test may be carried out either by a thermal conductivity tester or by a thermal imaging camera . The results in Table 2 show clearly that the friction material according to the invention presents a relative high thermal conductivity, quite higher than that one of a standard NAO friction material .

[0112] CONCLUS IONS

[0113] According to the experimental tests carried out it is evident that the "Hybrid material" for coated rotors forms a braking system according to the invention which improves : a ) Friction Stability b ) Particle Number and Particle Mass emission

[0114] Those characteristics are reached with reduction of material abrasiveness ( ratio Abrasive >7 and lubricant reduced compared with classical NAO) and increase of material thermal conductivity .

[0115] The coupling between this hybrid material according to the invention and a single layer coated rotor moreover improves Corrosion cleaning, Stiction tendency and Low frequency noise ( CG) .

[0116] Those characteristics are also linked with typology of rotor coating that is not corroded on the surface , since it is covered with a layer of alloyed steel

[0117] All the aims of the present disclosure are therefore ful filled .

[0118] Certain Terminology

[0119] Although certain braking devices , systems , and methods have been disclosed in the context of certain example embodiments , it will be understood by those skilled in the art that the scope of this disclosure extends beyond the speci fically disclosed embodiments to other alternative embodiments and / or uses of the embodiments and certain modi fications and equivalents thereof , like brake shows for braking systems based on brake drums . Use with any structure is expressly within the scope of this invention . Various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the assembly . The scope of this disclosure should not be limited by the particular disclosed embodiments described herein .

[0120] Conditional language , such as "can, " "could, " "might , " or "may, " unless speci fically stated otherwise , or otherwise understood within the context as used, is generally intended to convey that certain embodiments include or do not include , certain features , elements , and / or steps . Thus , such conditional language is not generally intended to imply that features, elements, and / or steps are in any way required for one or more embodiments.

[0121] Unless stated otherwise, the terms "approximately," "about," and "substantially" as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, in some embodiments, as the context may dictate, the terms "approximately", "about", and "substantially" may refer to an amount that is within less than or equal to 10% of the stated amount. Likewise, the term "generally" as used herein represents a value, amount, or characteristic that predominantly includes or tends toward a particular value, amount, or characteristic.

[0122] This disclosure expressly contemplates that various features and aspects of the disclosed embodiments can be combined with, or substituted for, one another. Accordingly, the scope of this disclosure should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow as well as their full scope of equivalents.

Claims

CLAIMS1. An asbestos free friction material composition comprising at least one filler, at least a fibrous material selected from the group consisting of inorganic fibers, organic fibers, any combination thereof, at least one organic binder, at least one lubricant and at least one or more abrasives, characterized in that it further comprises a non- negligible quantity of a thermally conductive, non-roundish, metallic powder substantially free of copper and / or of any metallic alloy including copper.

2. The asbestos free friction material composition according to claim 1, characterized in that said thermally conductive, non-roundish, metallic powder is an iron-based, ferrous metal powder.

3. The asbestos free friction material composition according to claims 1 or 2, characterized in that said thermally conductive, non-roundish, metallic powder is selected from the group consisting of: iron, an iron alloy, steel, stainless steel, any combination thereof.

4. The asbestos free friction material composition according to any of the preceding claims 1 to 3, characterized in that said thermally conductive, non- roundish, metallic powder is contained in the friction material composition in a quantity in volume comprised between 2%vol and 10%vol.

5. The asbestos free friction material composition according to any of the preceding claims 1 to 4, characterized in that said thermally conductive, non- roundish, metallic powder has a specific surface area of about 200-220 m2 / kg and a granulometric profile comprising:• a Dv(10) about 10-20,• a Dv(50) about 30-50• a Dv(90) about 57-60.

6. The asbestos free friction material composition according to any of the preceding claims 1 to 5, characterized in that, in combination with the presence of said thermally conductive, non-roundish, metallic powder, the at least one or more abrasives include at least a mild abrasive having a Mosh hardness <7 and at least a hard abrasive having a Mosh hardness >7, the ratio between the content in %vol of hard abrasives and the content in %vol of lubricants is comprised between about 0.1 and 1.5.

7. The asbestos free friction material composition according claim 6, characterized in that it has a substantially zero or reduced content in the hard abrasive zirconium oxide, the %vol of zirconium oxide on the total content of hard abrasives being lower than 5%.

8. The asbestos free friction material composition according to any of the preceding claims 6 or 7, characterized in that the ratio between the content in %vol of hard abrasives having a Mosh hardness >7 and the content in %vol of lubricants is comprised between about 0.16 and 0.36.

9. The asbestos free friction material composition according to any of the preceding claims 1 to 8, characterized in that it includes, in combination, listed in % by volume:Abrasive Mohs>7 2-8Abrasives Mohs <7 30-70Organic Binder (Resin) 6-10Organic additives 3-8Fibers 2-8Lubricants 6-15Metal powder 2-1010. The asbestos free friction material composition according to any of the preceding claims 1 to 9, characterized in that it includes organic additives comprising hydrophobic agents like PTFE or a wax, graphite, damping agents like rubber particles, friction dust.

11. The asbestos free friction material composition according to claim 10, characterized in that the ratio between the content of metallic powder and the content of organic additives is such that the thermal conductivity of the friction material composition is comprised between about 0.5 and 2 W / m°K, and preferably between 1.5 and 1.8 W / m°K.

12. A friction element having a friction layer or block made with a friction material composition according to any one of the preceding claims 1 to 11.

13. A friction element according to claim 12, characterized in that it is a brake pad including a metal support and a friction layer or block having a thermal conductivity comprised between about 0.5 and 2 W / m°K, and preferably between 1.5 and 1.8 W / m°K.

14. A braking system comprising a member to be braked, constituted by a brake disc or brake drum made of cast iron or steel and at least one braking member constituted by a brake pad or brake shoe, adapted to cooperate by friction with the member to be braked, characterized in that the braking member has a friction layer intended to cooperate with the member to be braked made of a friction material composition according to claims from 1 to 11.

15. A braking system comprising a member to be braked, constituted by a brake disc made of cast iron and at leastone braking member constituted by a brake pad, adapted to cooperate by friction with a friction surface of the brake disc, characteri zed in that the brake pad has a friction layer intended to cooperate with the friction surface of the brake disc made of a friction material composition according to claims from 1 to 11 and, in combination, the friction surface of the brake disc is coated with a single layer coating of a Fe alloy with Ni and / or Cr .16 . A braking system according to claim 15 , characteri zed in that said single layer coating of said friction surface of the brake disc and cooperating with the brake pad consists of a stainless-steel alloy .

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