Improved friction material composition and associated friction element

Abstract

An asbestos-free friction material composition and an associated brake pad for a vehicle, in particular an electric vehicle, where the composition comprises at least one filler, at least one fibrous material, at least one binder, at least one titanate, at least one barite and at least one silicone rubber in combination with at least one expanded or foamed silicate.

Description

[0001] Cross - reference to related applications

[0002] This patent application claims the priority of Italian Patent Application No. 102022000023793, filed on November 18, 2022, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a friction material composition, which is particularly suitable for manufacturing friction layers / friction pads for friction elements, such as brake elements to be incorporated in, for example, vehicle braking systems.

[0004] The present invention also relates to associated friction elements made of such friction material composition, such as brake pads or brake shoes for vehicles, and is particularly but not exclusively applicable to electric vehicles.

[0005] The friction material composition of the present invention is asbestos - free, belongs to the so - called NAO (“Non - Asbestos Organic”) type and is substantially copper - free. Background art

[0006] With the rapid development of the modern transportation industry, the number of electric vehicles is increasing day by day.

[0007] Replacing combustion engines with electric motors results in much quieter vehicles. This has led to a higher focus on the noise generated by other automotive components, such as those generated by brake pads used in braking systems. Therefore, brake pads for electric vehicles need to improve the NVH (noise, vibration, harshness) standards for driving comfort.

[0008] Also for this purpose, it is known from an article published in the journal SAE 2007 that mixed titanates of different natures are used together with a large amount of copper (about 5 wt% or more).

[0009] Unfortunately, when copper is used in a friction material composition designed to produce brake elements, copper may be regarded as a contaminant material. The states of Washington and California have prohibited the sale of friction materials with a copper content exceeding 5% since 2021 and have prohibited the sale of friction materials with a copper content exceeding 0.5% since 2023.

[0010] In addition to copper regulations, the emergence of vehicle electrification has made vehicle quieting a crucial goal and requires the use of developed friction materials to achieve friction mechanisms in use, such as the generation of no low - frequency noise. The friction mechanism that causes low - frequency noise is known and is known as the “stick - slip” phenomenon.

[0011] In particular, the stick-slip phenomenon can cause the generation of so-called "creep flutter" low-frequency noise, especially at very low vehicle speeds. This is a typical example of self-excited brake vibration caused by the alternating adhesion or attachment and subsequent sliding of the brake pads on the brake disc during braking, and thus the coefficient of friction continuously varies between the static (adhesion phase) value and the dynamic (sliding phase) value.

[0012] Various solutions are known in the art to attempt to reduce this phenomenon, but they cannot completely solve the problem or have additional drawbacks.

[0013] EP0959262 discloses a disc brake pad that can use a composition containing a fiber substrate other than asbestos, a binder, and a friction modifier to reduce creep flutter, wherein the binder wholly or partly comprises a modified silicone resin, and wherein the friction material composition combinatorially comprises between 0.5% and 20% by volume of zeolite as part of the friction modifier. The content of the modified silicone resin is in an amount of 3% to 30% by volume of the total composition and is obtained by reacting an oil or silicone rubber with a novolac-type phenolic resin. This results in the material being expensive and difficult to produce.

[0014] On the other hand, WO2019120648 discloses hybrid friction lining materials and brake pads made therefrom, wherein an attempt is made to combine the positive properties of a low-steel friction lining material (so-called low-steel (LS) friction lining) and an asbestos-free organic friction lining material. In a preferred embodiment, such a hybrid friction material comprises: 15% to 22% by weight (by weight), in particular 17% to 20% by weight, of at least one binder; 5% to 11% by weight of organic fibers or a mixture of organic fibers; 1% to 20% by weight, in particular 8% to 14% by weight, of at least one additional organic compound; zero or 8% to 16% by weight of inorganic fibers or a mixture of inorganic fibers; 10% to 40% by weight of at least one inorganic oxide; 6% to 12% by weight of at least one inorganic silicate; 13% to 15% by weight of sulfur or at least one inorganic sulfur compound; 10% to 16% by weight of carbon or at least one material substantially comprising carbon, which is particularly selected from the group consisting of natural graphite, synthetic graphite, petroleum coke, dry petroleum coke, carbon black, and any mixture thereof; 1% to 1.5% by weight of at least one filler selected from the group of inorganic hydroxides, in particular calcium hydroxide; and zero up to 1% by weight of at least one metal, in particular iron or an iron alloy. However, such a hybrid material produces a compromising behavior in terms of braking performance and comfort, which may not be optimal or ideal enough for many applications.

[0015] CN106015399 discloses a friction material for a brake lining of an electric vehicle. The friction material comprises, by weight: 25 to 30 parts of carbon fiber, 10 to 15 parts of aramid fiber, 40 to 50 parts of nitrile rubber, 20 to 30 parts of styrene-butadiene rubber, 10 to 20 parts of carbon black, 5 to 12 parts of composite mineral fiber, 1 to 3 parts of sulfur, 1 to 4 parts of vermiculite, 2 to 7 parts of epoxy resin, 6 to 15 parts of barium sulfate, 3 to 8 parts of graphite, 0.5 to 1 part of accelerator, 2 to 4 parts of stabilizer, and 1 to 2 parts of water. However, the brake lining formed from this friction material does not show any overcoming of disadvantages in terms of reducing noise and particulate emissions and improving friction stability. Summary of the Invention

[0016] The object of the present invention is to develop a new asbestos-free friction material composition that can overcome the disadvantages of the prior art. In particular, the presently disclosed subject matter aims to provide an asbestos-free friction material composition that significantly reduces the tendency of the friction block to adhere to the surface of a mating friction pair, such as a brake disc.

[0017] Accordingly, the present invention relates to a friction material composition as defined in the appended claims.

[0018] Another object of the present invention is to provide a friction element, particularly a brake lining or a brake shoe, comprising the friction material composition.

[0019] The present disclosure shows how, starting from any known friction material formulation, such as the friction material formulation proposed by Otsuka in the SAE 2007 paper, adding an appropriate combination of inorganic materials and elastomeric foam (expanded) materials while substantially eliminating copper can not only meet the more stringent US copper regulations, but most importantly, allows for the mitigation of the stick-slip phenomenon.

[0020] In particular, the expanded material or foam material used according to the present invention must have a layered structure or a tunnel-like structure. A comparison with a substantially identical NAO composition that contains 5% of Cu instead of this expanded material or foam material is also included in the present disclosure.

[0021] In view of the disclosure provided below, other features and advantages of the disclosed subject matter will become apparent whether or not explicitly mentioned.

[0022] Accordingly, the present disclosure relates to a friction material composition belonging to the class of friction materials known as NAO (non-asbestos organic), which aims to obtain improved stick-slip behavior for the benefit of the creep flutter phenomenon and friction stability with respect to known NAO friction compositions.

[0023] In fact, different from known NAO friction compositions, the disclosed friction material composition further includes an appropriate amount of silicone rubber and expanded calcium silicate, such as vermiculite, to replace copper and combinations thereof. In addition to silicone rubber and expanded calcium silicate, expanded mixed silicates of aluminum and magnesium can also be used.

[0024] Although less effective results are obtained, combinations of silicone rubber with expanded mixed silicates of aluminum and magnesium can also be used.

[0025] Since any ordinary (i.e., unmodified) silicone rubber available on the market, which is an inexpensive material, is combined with expanded silicate, preferably calcium silicate, and the expanded silicate is also an inexpensive raw material available on the market, the disclosed friction material composition results in reduced stick-slip phenomena, which in turn can positively affect the creep flutter noise.

[0026] Meanwhile, copper and any of its alloys are substantially absent. For "substantially absent" herein and hereinafter, it is intended that the residual content of Cu or Cu alloy in the disclosed friction material is less than 0.5% by weight calculated based on the total weight of the friction material composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other features 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 drawings, in which:

[0028] - Figure 1 A three-quarter perspective view is schematically shown as viewed from above a device called a tribometer and used to test the tribological properties of friction material elements as will be described.

[0029] - Figure 2 The same three-quarter perspective view is schematically shown as viewed from above the same device in Figure 1 to which a fluid-tight sealed climate chamber has been added in order to perform tribological tests under controlled temperature and humidity conditions.

[0030] - Figure 3 and Figure 4 show a graph illustrating the tribological test results under different humidity conditions obtained using the device for a friction material block made of a first friction material composition of the present invention provided herein as a comparative material Figure 1 and 2 wherein Figure 3 shows the behavior of the coefficient of friction over time, and Figure 4 shows in bar graph the amplitude and number of stick-slip events;

[0031] - Figure 5 andFigure 6 shows a graph of tribological test results under different humidity conditions obtained using a device for a friction material block made of a second friction material composition that illustrates the present invention provided herein as a non-limiting working example but not the best one Figure 1 and Figure 2 shows the behavior of the coefficient of friction over time, and Figure 5 shows the amplitude and number of stick-slip events in a bar graph; Figure 6

[0032] - Figure 7 and Figure 8 shows a graph of tribological test results under different humidity conditions obtained using a device for a friction material block made of a third friction material composition prepared according to the prior art and containing copper as one of the components provided herein as a reference material Figure 1 and Figure 2 shows the behavior of the coefficient of friction over time, and Figure 7 shows the amplitude and number of stick-slip events in a bar graph; Figure 8

[0033] - Figure 9 and Figure 10 shows a graph of tribological test results under different humidity conditions obtained using a device for a friction material block made of a fourth friction material composition of the present invention but not the best one Figure 1 and Figure 2 shows the behavior of the coefficient of friction over time, and Figure 9 shows the amplitude and number of stick-slip events in a bar graph; Figure 10

[0034] - Figure 11 and Figure 12 shows a graph of tribological test results under different humidity conditions obtained using a device for a friction material block made of a fifth friction material composition of the present invention provided herein as a preferred working example Figure 1 and Figure 2 shows the behavior of the coefficient of friction over time, and Figure 11 shows the amplitude and number of stick-slip events in a bar graph; Figure 12

[0035] - Figure 13 is a summary bar graph comparing the average amplitude of stick-slip events detected by the device of Figure 1 and Figure 2 for each of the five friction material compositions tested; and

[0036] - Figure 14 ​​​​Shows a schematic diagram of a standard AK-Master test on a friction element made of a friction material composition according to a preferred embodiment of the present invention, the test having tribological tests as shown in Figure 11 and Figure 12 as shown. Detailed Description

[0037] More specifically, the disclosed asbestos-free friction material composition includes at least one filler, at least one fiber material, at least one binder, at least one lubricant, at least one expanded (or foamed) silicate, and preferably at least one or more abrasives.

[0038] Preferably, the disclosed asbestos-free friction material composition further includes at least one silicone rubber combined with, i.e., bonded to, at least one expanded (or foamed) silicate.

[0039] The silicone rubber can preferably be a common, commercial, unmodified silicone rubber having a density included between about 1.33 g / cm 3 and about 1.39 g / cm 3 and having a particle size, i.e., particle size distribution, such that the average D included between 450 micrometers (μm) and 550 micrometers (μm) 50 .

[0040] Herein and hereinafter, "particle size distribution D 50 " corresponds to the value of the particle diameter at 50% in the cumulative distribution.

[0041] The expanded (or foamed) silicate can be any expanded silicate that is chemically compatible with the other raw materials included in the friction material mixture and is preferably selected from the group including expanded Al, Mg silicates, expanded vermiculite, expanded calcium silicate, and any mixture thereof.

[0042] Most preferably, more than one expanded silicate or foamed silicate is used in the disclosed asbestos-free friction material, so the more than one expanded silicate or foamed silicate can combinatorially include expanded calcium silicate and expanded Al, Mg silicate or expanded vermiculite.

[0043] Expanded calcium silicate can be commercially available as a lightweight filler for, for example, concrete mixtures used in building structures. For example, expanded calcium silicate can be obtained according to US3998650A.

[0044] Most preferably, the expanded calcium silicate used in the present invention can have an apparent density lower than 0.5 gr / cm 3 .

[0045] According to a preferred embodiment of the present invention, the expanded Al, Mg silicate / expanded vermiculite used according to the present disclosure may preferably have an apparent density included between 0.08 gr / cm 3 and 0.12 gr / cm 3 (i.e., between 80 kg / m 3 and 120 kg / m 3 ).

[0046] The expanded Al, Mg silicate / expanded vermiculite used according to the present disclosure may have a particle size distribution such that D 50 is included between 0.8 mm and 1 mm.

[0047] The ratio between the weight-based content of silicone rubber and the weight-based content of expanded / foamed silicate may preferably be 1:3 in the case of expanded Al, Mg silicate or expanded vermiculite and may preferably be 1:2 in the case of expanded calcium silicate.

[0048] When used together, the ratio between the weight-based content of expanded calcium silicate and the weight-based content of expanded Al, Mg silicate (or expanded vermiculite) may preferably be 2:3.

[0049] In addition to silicone rubber and expanded silicate, other components of the disclosed friction material composition mentioned above may be components used in friction materials already known in the art.

[0050] In particular, at least one fiber material may be selected from the group comprising inorganic fibers, organic fibers, metal fibers and any combination thereof.

[0051] Preferably, at least one fiber material comprises organic fibers selected from the group comprising polyacrylic fibers, polyaramid fibers, aromatic polyamide fibers, cellulose fibers and mixtures thereof.

[0052] Organic fibers may preferably but not exclusively be included as part of an organic binder in the friction material composition of the present disclosure, as they may have the main purpose of enhancing its strength under the operating conditions of brake pads / shoes that can be manufactured from the friction material composition of the present disclosure.

[0053] At least one binder is preferably an organic binder and may be selected from the group comprising phenolic resins, epoxy resins, silicone resins, modified phenolic resins, melamine resins, polyamide resins and mixtures thereof.

[0054] At least one lubricant may preferably but not exclusively include a sulfide-based lubricant selected from the group comprising metal sulfides of Sn, Zn, Fe, Mo and mixtures thereof.

[0055] Many materials can be used as organic fillers or inorganic fillers. The inorganic fillers can be selected from the group including the following: barite, mineral fibers, glass fibers, rock wool, layered silicates other than vermiculite (such as mica, talc, etc.), inorganic hydroxides of calcium, magnesium, potassium, and any mixture thereof.

[0056] In addition, according to one aspect of the present invention, as at least one filler, the friction material composition of the present disclosure must include one or more titanates selected from commercially available titanates.

[0057] The content of the titanate can preferably but not exclusively be about 20% by weight of the total weight of the friction composition, and can be any value included between 8% by weight and 25% by weight of the total weight of the friction composition.

[0058] At least one or more abrasives include at least one soft abrasive having a Mohs hardness lower than 7 and at least one hard abrasive having a Mohs hardness higher than 7.

[0059] The ratio of the content by weight of the soft abrasive to the content by weight of the hard abrasive ranges from 1:1 to 4:1 and can preferably be 2:1.

[0060] The hard abrasive (i.e., having a Mohs hardness higher than 7) preferably but not exclusively has a slightly rounded shape, and is preferably but not exclusively selected from the group including zirconia, alumina, corundum, silicon carbide, tungsten carbide, zirconium carbide, zirconium silicate, boron nitride, and any mixture thereof.

[0061] The soft abrasive (i.e., having a Mohs hardness lower than 7) can preferably but not exclusively be selected from the group including magnesia, chromite, magnetite, hematite, quartz, zinc oxide, tin oxide, barium sulfate, silicates, fluorides, and any mixture thereof.

[0062] According to a preferred embodiment of the present invention, the disclosed friction material composition does not contain copper.

[0063] Herein and hereinafter, the expression "does not contain copper" should be understood to imply that the content of copper and / or copper-containing materials such as copper alloys is 0.5% by weight or less than 0.5% by weight.

[0064] When present in the disclosed friction material composition, at least one metal or mixture of metals does not include copper and / or any copper alloy, but is selected from the group including iron, steel, stainless steel, tin, zinc, and any alloy thereof in the form of powder or fiber.

[0065] In addition, the disclosed friction material composition can include organic additives selected from the group including polytetrafluoroethylene, friction powders, cashew shell powder, rubbers other than silicone rubber such as NBR, SBR, etc.

[0066] In another embodiment of the present invention, the average friction material composition can be as follows (% is by weight - including lubricants as mentioned above in "inorganic fillers" and excluding barite, according to one aspect of the present disclosure, barite must be present alone or in combination with other fillers):

[0067]

[0068] The present invention finally also relates to a friction element, in particular a brake lining or a brake shoe, which presents a friction material layer made of the above-mentioned friction material composition.

[0069] The present invention also relates to a braking system, which includes a member to be braked constituted by a brake disc or a brake drum made of cast iron or steel and at least one braking element constituted by a brake lining or a brake shoe, the at least one braking element being designed to cooperate with the member to be braked by means of friction, wherein the braking member presents a friction layer designed to cooperate with the member to be braked and made of the above-mentioned friction material composition.

[0070] Exemplary modes of carrying out the teachings of the present disclosure

[0071] Inventive examples and comparative examples are reported herein by way of illustration and are not intended to limit the present invention.

[0072] Example 1

[0073] Prepare five formulations labeled "F1", "F2", "F3", "F4" and "F5" according to Table 1 below. The components shown in Table 1 are expressed as percentage values by weight of the total weight of the composition.

[0074] The friction material compositions according to the present invention are indicated by "F1" and "F5" and according to a preferred embodiment of the present invention, they differ only in that a second expanded silicate is added to the basic formulation of "F1".

[0075] The comparative friction material compositions are indicated as "F2", "F3" and "F4".

[0076] "F3" is a reference friction material composition and basically corresponds to the friction material disclosed by Otsuka in SAE2007, except that the copper initially disclosed in SAE2007 has been eliminated and replaced by a small amount of additives in other components, especially barite.

[0077] "F2" and "F4" have the same composition as the two inventive mixtures "F1" and "F5", except that:

[0078] - In "F2", silicone rubber is missing and compensated with barytes in the corresponding added amount. Barytes is an inert inorganic filler; and

[0079] - In "F4", silicone rubber is present but any expanded silicate is missing and compensated with barytes in the corresponding added amount.

[0080] The total amount of each column in Table 1 is 100 (100 wt%):

[0081] Table 1

[0082]

[0083] The components shown in Table 1 are uniformly mixed in a horizontal mixer (e.g., a mixer of the Loedige type) and molded in a mold at a temperature of 160 °C under a pressure of 20 tons for 3 minutes, and then cured at a temperature ranging from 150 °C to 400 °C for 10 minutes to 10 hours, thereby producing five series of friction material blocks for each of the different compositions reported in Table 1.

[0084] Each of the obtained friction material blocks is made integral with the same metal support including a flat steel plate (backing plate) to form a vehicle brake lining.

[0085] Example 2: Tribological tests

[0086] For each series of brake linings having the same friction material composition as each of the friction material compositions reported in Table 1 produced as in Example 1, a first number of friction material blocks have been tested using the following test parameters by means of the device (friction meter) as shown in Figure 1 and Figure 2 :

[0087] - Rotor speed: 0.1 rpm to 5000 rpm

[0088] - Torque: 0.01 Nm to 5 Nm

[0089] - Maximum load force: 2000 N.

[0090] Refer to Figure 1 and Figure 2 , the test device as a whole is indicated by the reference numeral 1. In Figure 1 and Figure 2 , the test device 1 and all other elements / components to be described hereinafter are illustrated only by way of example and only in a purely schematic manner, without any pretense of realism.

[0091] The test device 1 includes an electric rotor 2 which is configured to receive a known brake disc 3 during testing, such that the brake disc 3 rotates, for example, in the direction of the arrow at a predetermined speed included between 0.5 rpm and 5000 rpm.

[0092] The device 1 also includes a sample holder 4 which is configured to receive, one at a time during testing, a brake pad 5 or a friction material block of the brake pad 5. The brake pad 5 is, where appropriate, the brake pad produced in Example 1. The sample holder 4 is held by a shaft 6 which is configured to move up and down in the direction of the arrow according to Figure 1 and Figure 2 so as to press the brake pad / friction material block against the brake disc with a predetermined load force F of up to 2000 Nw. The shaft 6 is connected in a known manner to known force and torque sensors which are indicated schematically as a single block numbered 7 overall.

[0093] Finally, the device 1 also includes a climate chamber 8 ( Figure 2 ) which can be mounted in the device 1 so as to enclose / seal the brake disc 3 and the brake pad / friction pad 5 therein. The climate chamber 8 is configured to produce a controlled humidity within a controlled environment, which controlled humidity is capable of varying between 10% relative humidity (RH) and 90% relative humidity (RH).

[0094] Thus, by applying a known vertical pressing force to the holder 4 and by rotating the rotor 2 at a known speed, it is possible to brake the rotor 2 with a test sample held by the sample holder under different humidity conditions and it is possible to detect the torque by means of the sensor 7. For example, the test can be carried out as follows:

[0095] - Apply the pressing force F so as to press the sample 5 against the stationary brake disc 2;

[0096] - Start rotating the brake disc 3 by rotating the electric rotor 2;

[0097] - Measure the torque and the force by means of the sensor 7;

[0098] - Calculate the instantaneous coefficient of friction CoF during the entire duration of the test in real time.

[0099] Multiple samples measuring 10 mm × 10 mm to be mounted on the sample holder 4 are cut from the brake pads / friction pads produced in Example 1, and the tests are carried out using a cast iron brake disc 3. For each friction material, a new disc is used for each measurement. The instantaneous coefficient of friction is calculated using the following formula:

[0100] [1]

[0101] Wherein:

[0102] - Tz is the measured torque;

[0103] - Fz is the load force;

[0104] - Reff is the effective radius at which the sample is mounted on the sample holder;

[0105] During testing, especially at higher levels of relative humidity, at low rotational speeds there will be stick-slip events, where the coefficient of friction instantaneously shifts between the static coefficient of friction CoF s and the dynamic coefficient of friction CoF d resulting in peaks in the graph of CoF versus time. Thus, the magnitude of the change in the coefficient of friction between static and dynamic (the magnitude of the peak) can be calculated instantaneously using the following formula:

[0106] [2] ΔCoF = CoF s - CoF d

[0107] Thus, with the aid of device 1 and the computer, graphs of the coefficient of friction over time and at different levels of relative humidity can be obtained for each type of test sample and thus for each friction material composition listed in Table 1, as shown in Figure 3 , Figure 5 , Figure 7 , Figure 9 , and Figure 11 .

[0108] The test for each sample of the different friction material compositions is repeated three times and the sum of the values obtained (amplitude and number of stick-slip events) is plotted in the bar graphs of Figure 4 , Figure 6 , Figure 8 , Figure 10 , and Figure 12 .

[0109] Example 3: Discussion of test results:

[0110] By carefully comparing the graphs of Figure 4 , Figure 6 , Figure 8 , Figure 10 , and Figure 12 , it is evident that, considering the tendency to experience stick-slip events, when compared to the reference material F3, material F5 ( Figure 12 ) is the best material: the number of events is quite low and the events only occur when the level of relative humidity is relatively high (up to 60%). Additionally, the magnitude of the events is quite small, i.e., the coefficient of friction tends to remain substantially constant. In contrast, in material F3 (Figure 8 ) In it, the number and amplitude of the stick-slip events are quite high, and the events have started at 40% relative humidity, which is a "normal" level in the natural environment (i.e., on a normal day, neither dry nor wet), allowing it to be inferred that the reference composition frequently presents stick-slip events under any weather conditions.

[0111] Figure 4 and Figure 10 respectively show the behaviors of Material F4 that contains only silicone rubber in addition to the reference material and Material F2 that contains only expanded Al, Mg silicate (expanded vermiculite) in addition to the reference material.

[0112] Material F4 added with silicone rubber shows ( Figure 4 ) results comparable to those of the reference material F3.

[0113] Material F2 added with expanded vermiculite (or other equivalent Al, Mg silicates) does not present stick-slip events at 40% relative humidity; furthermore, at high relative humidities, Material F2 only has better results (compared to F3) at 60% relative humidity, while at higher humidities, it has comparable behavior.

[0114] Finally, Material F1 added with both silicone rubber and expanded vermiculite shows significantly worse results compared to the previous material, because Material F1 already shows stick-slip events at 40% relative humidity, but when compared to the reference material F3, the number of events and most importantly the amplitude of the events are lower, and especially significantly lower at 60% relative humidity and above 60% relative humidity.

[0115] It can be inferred from the test results that:

[0116] - The influence of the addition of expansion materials and elastic materials on stick-slip events and accordingly on the generation of the creeping flutter phenomenon is quite unpredictable;

[0117] - The addition of elastic materials alone such as silicone rubber obviously does not have a significant effect;

[0118] - On the contrary, the addition of expanded silicates alone, such as expanded vermiculite for example, has a positive effect and leads to the disappearance of stick-slip events at the relative humidity levels most common in the natural environment;

[0119] - The simultaneous addition of silicone rubber and expanded silicate controls stick-slip events at all different humidity levels;

[0120] - The best results are obtained when two different expanded silicates are used in combination with silicone rubber, where the stick-slip events and the corresponding creeping flutter phenomenon are significantly reduced until almost disappearing.

[0121] Finally, from Figure 13 In the overview graph comparing only the average amplitude of the stick-slip events (and thus representing only a partial overview of the relevant physical phenomenon) shown in, it is evident that all materials F2, F4, and F5 present better results compared to the reference material F3. Clearly, material F2 (the present invention) shows a behavior similar to that of material F4 (not the present invention), however, as emphasized above, material F2 does not present stick-slip events at 40% relative humidity, while material F4 presents such events, even if in a reduced number.

[0122] Example 4: AK Master test

[0123] To understand whether the addition of silicone rubber and metal silicate might affect the braking performance, according to the known AKM Master test, an efficiency test was carried out on batches of brake pads containing all these added materials produced in the manner described in Example 1 using material F5, including: parking brake, braking at different fluid pressures, "cold braking" (<50 °C) evaluation, road simulation braking, two sets of high-energy braking (first fade test) interspersed with a series of recovery brakings. From this test, it is also possible to infer, in a manner known to those skilled in the art, the general behavior of the friction material mixture composition and the coefficient of friction during the entire test duration.

[0124] The results obtained are shown in Figure 14 which schematically represents the extraction of the important data of the experimental curves obtained. Figure 14 In the two shaded graphs in, the trends of the different steps of the test along the minimum and maximum values of the observed (calculated) coefficient of friction are shown, while the solid graph shows the trends of the different steps of the test along the average value of the coefficient of friction.

[0125] The experimental results show that the presence of the three additional raw materials basically does not affect the braking performance, and as can be understood, the coefficient of friction does not change significantly and in any case remains within the range of acceptable values at all steps of the test.

[0126] Thus, all the objectives of the present disclosure are achieved.

[0127] Specific terms

[0128] Although specific braking devices, systems, and methods have been disclosed in the context of specific example embodiments, those skilled in the art will understand that the scope of the present disclosure extends to other alternative embodiments and / or uses of the embodiments beyond the specifically disclosed embodiments and their specific modifications and equivalents, such as braking displays for drum-based braking systems. The use of any structure is clearly within the scope of the present invention. The various features and aspects of the disclosed embodiments may be combined with or substituted for one another to form different modes of the components. The scope of the present disclosure should not be limited by the specific disclosed embodiments described herein.

[0129] Unless specifically stated otherwise or understood in the context in which it is used, conditional language such as "able to", "can", "may", or "could" generally intends to convey that a particular embodiment includes or does not include a particular feature, element, and / or step. Thus, such conditional language generally does not imply that the feature, element, and / or step is required in any way for one or more embodiments.

[0130] Unless otherwise specified, as used herein, the terms "about", "approximately", and "substantially" mean an amount close to the stated amount that still performs the desired function or achieves the desired result. For example, in some embodiments, as the context may indicate, the terms "about", "approximately", and "substantially" may refer to an amount within a range of less than or equal to 10% of the stated amount. Similarly, as used herein, the term "generally" represents mainly including or tending to a particular value, amount, or characteristic of a value, amount, or characteristic.

[0131] The present disclosure clearly contemplates that the various features and aspects of the disclosed embodiments may be combined with or substituted for one another. Accordingly, the scope of the present disclosure should not be limited by the above-described specific disclosed embodiments, but should be determined only by a reasonable interpretation of the appended claims and their full scope of equivalents.

Claims

1. An asbestos-free friction material composition, comprising: At least one filler; At least one fiber material selected from the group consisting of inorganic fibers, organic fibers, metal fibers, and any combination thereof; at least one organic binder; at least one lubricant; and / or at least one or more abrasives, characterized in that the asbestos-free friction material composition further comprises at least one expanded or foamed silicate.

2. The asbestos-free friction material composition according to claim 1, characterized in that, The asbestos-free friction material composition comprises, in combination: - at least one silicone rubber, and - the at least one expanded or foamed silicate.

3. The asbestos-free friction material composition according to claim 2, characterized in that, The silicone rubber is unmodified silicone rubber, and the silicone rubber has a density including between about 1.33 g / cm 3 and about 1.39 g / cm 3 and has a particle size distribution such that it has an average D including between 450 micrometers (μm) and 550 micrometers (μm). 50 .

4. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The expanded or foamed silicate is chemically compatible with the other raw materials comprised in the friction material composition and is selected from the group consisting of expanded Al, Mg silicate, expanded vermiculite, expanded calcium silicate, and any mixture thereof.

5. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The asbestos-free friction material composition comprises a single expanded or foamed silicate, and wherein the expanded or foamed silicate is expanded calcium silicate.

6. The asbestos-free friction material composition according to any one of the preceding claims 1 to 4, characterized in that The asbestos-free friction material composition comprises a single expanded or foamed silicate, and wherein the expanded or foamed silicate is expanded Al, Mg silicate or expanded vermiculite.

7. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The asbestos-free friction material composition comprises, in combination: - at least one silicone rubber, - at least one expanded aluminum silicate or expanded vermiculite, - at least one expanded calcium silicate.

8. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The expanded Al, Mg silicate or expanded vermiculite has an apparent density including between 0.08 gr / cm 3 and 0.12 gr / cm 3 (i.e., between 80 kg / m 3 and 120 kg / m 3 ).

9. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The expanded Al, Mg silicate or expanded vermiculite has a particle size distribution such that D 50 is included between 0.8 mm and 1 mm.

10. The asbestos-free friction material composition according to claim 2, characterized in that, The ratio between the content by weight of the silicone rubber and the content by weight of the expanded or foamed silicate is 1:3 in the case of expanded Al, Mg silicate or expanded vermiculite, and 1:2 in the case of expanded calcium silicate.

11. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, When expanded calcium silicate and expanded Al, Mg silicate or expanded vermiculite are present together simultaneously, the ratio of the content by weight of the expanded calcium silicate to the content by weight of the expanded Al, Mg silicate or expanded vermiculite is 2:

3.

12. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The at least one fiber material comprises: organic fibers selected from the group consisting of polyacrylic fibers, polyaramid fibers, aromatic polyamide fibers, cellulose fibers, and any mixture thereof; and / or inorganic fibers or metal fibers.

13. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The asbestos-free friction material composition comprises at least one lubricant, and the at least one lubricant comprises a sulfide-based lubricant selected from the group consisting of metal sulfides of Sn, Zn, Fe, Mo, and mixtures thereof.

14. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The asbestos-free friction material composition comprises at least one titanate, and the amount of the at least one titanate preferably comprises between 8% by weight and 25% by weight calculated based on the total weight of the composition.

15. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The asbestos-free friction material composition does not contain copper and does not contain any copper alloy.

16. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that The asbestos-free friction material composition comprises at least one metal other than copper and copper alloy, and the at least one metal is selected from the group consisting of iron, steel, stainless steel, tin, zinc in powder or fiber form, and any alloy thereof.

17. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The at least one filler is an inorganic filler and at least comprises barite (barium sulfate).

18. The asbestos-free friction material composition according to any one of the preceding claims, characterized in that, The asbestos-free friction material composition comprises the following components in weight percentages calculated based on the total weight of the friction material composition:

19. A friction element having a friction layer made of the friction material composition according to any one of the preceding claims.

20. The friction element according to claim 19, characterized in that, The friction element is a brake lining or a brake shoe.

21. A braking system, the braking system comprising a member to be braked constituted by a brake disc or a brake drum made of cast iron or steel and at least one braking member constituted by a brake lining or a brake shoe, the braking member being adapted to cooperate with the member to be braked by friction, characterized in that, The braking member has a friction layer made of the friction material composition according to claims 1 to 18 and is intended to cooperate with the member to be braked.

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