Friction material and corresponding disc brake pad

Abstract

The present invention relates to a friction material, a corresponding disc brake pad, and a brake system comprising said pad, which suppresses or significantly reduces the so-called "creep groan" phenomenon. More specifically, the present invention relates to a graphite-free friction material comprising: 20% to 30% by volume of one or more abrasives; 10 to 20% by volume of coke; up to 10% by volume of one or more metal sulfides; up to 20% by volume of one or more metals and / or metal alloys and / or intermetallic compounds in powder form; up to 40% by volume of a fibrous material consisting of aramid fibers and steel fibers; 10% to 20% by volume of a phenolic resin as a binder; and up to 10% by volume of one or more fillers selected from calcium hydroxide, friction powder, PTFE, and fluorite.

Description

[Technical field]

[0001] The present invention relates to a friction material, a disc brake pad having a friction layer made of the friction material, and a brake system having the pad. [Background technology]

[0002] Asbestos-free and heavy metal-free friction materials for brake pads typically contain the following types of components: fibrous material consisting of inorganic and / or organic and / or metallic fibers; one or more abrasives; one or more binders; one or more fillers; and one or more lubricants or friction modifiers. The most widely used lubricant is graphite, and an example of a graphite-containing friction material is described in CN110878802.

[0003] However, vehicles using brake pads manufactured using the aforementioned friction materials may develop a disturbing vibration phenomenon, the so-called "creep grow", which is of paramount importance in the automotive field, particularly in internal combustion and / or electric vehicles, with regard to NVH behavior (noise, vibration and impact noise), also known as NVH performance level.

[0004] Such a phenomenon is known as the "stick-slip" effect (or simply "stick-slip"), caused by the brake pads in contact with the brake disc surface alternating between adhesion and slip, i.e. repeated switching between static and kinetic friction. Stick-slip causes a dynamic response of the vehicle, particularly in terms of annoying noise and vibrations, which can be perceived in the passenger compartment.

[0005] Stick-slip, and thus the vehicle response known as "creep groove", occurs when a static or near-static braking torque is present under near-zero speed conditions, for example, upon gradually releasing the brake pedal going downhill or when starting off in an automatic transmission.

[0006] The alternating static and kinetic friction strongly links the behavior of the brake system with respect to the "creep-groon" phenomenon to the environmental conditions, especially temperature and humidity.

[0007] Various proposals are known in the art aimed at mitigating the "creep grow" phenomenon and reducing the noise and vibration associated with vehicle braking systems.

[0008] For example, EP 959 262 describes brake pads obtained using a composition comprising a modified silicone resin as binder and a zeolite as friction modifier. A particular composition described in such document contains graphite.

[0009] Other proposals are described, for example, in WO2020 / 189649 and JP 2002-266915, all of the specific compositions described therein also containing graphite.

[0010] Nevertheless, there is an increasing need to develop further compositions for friction materials that can suppress or at least significantly reduce the "creep grow" phenomenon.The problem underlying the present invention is therefore to provide a friction material for brake pads that reduces the noise and vibration associated with the braking system of an automobile, improving the NVH behavior, as represented by the measurement of vehicle comfort. Summary of the Invention

[0011] The above-mentioned problems are solved by the friction material, the disc brake pad and the braking system as outlined in the appended claims, the definitions of which form an integral part of this specification.

[0012] A first object of the present invention is a friction material comprising: 20-30% by volume of one or more abrasives; 10 to 20 volume percent, coke; up to 10% by volume of one or more metal sulfides; up to 20% by volume of one or more metals and / or metal alloys and / or intermetallic compounds in powder form; Fibrous materials containing up to 40% by volume of aramid and steel fibres; 10% to 20% by volume of a phenolic resin as a binder; up to 10% by volume of one or more fillers selected from calcium hydroxide, friction powder, PTFE, and fluorspar; Here, the friction material does not contain graphite.

[0013] A further object of the invention is a pad for a disc brake comprising a friction layer intended to cooperate with a disc of a disc brake, said friction layer being made of a friction material as defined above.

[0014] Another object of the invention is a braking system for a disc brake comprising a disc and a pad consisting of a friction layer intended to cooperate with the disc, said friction layer being made of the friction material defined above.

[0015] It has been surprisingly found that the brake system of the present invention, which comprises a pad having a friction layer made of the above-mentioned friction material composition, exhibits a significant reduction in "creep growth" both in the intensity of the phenomenon and its duration at various temperatures and various relative humidity levels. Thus, the friction material according to the present invention has proven to be particularly effective in improving the NVH behavior (noise, vibration and impact noise) and thus the comfort level of the vehicle.

[0016] Further features and advantages of the invention will become more apparent from the description of some exemplary embodiments given below, by way of non-limiting example. [Brief description of the drawings]

[0017] [Figure 1]FIG. 1 shows a “main effect plot” diagram relating to the average evaluation value (so-called “average creep growth score”) of the “creep growth” phenomenon for friction material A of the present invention and comparative friction materials B, C, and D, which were performed by changing the graphite concentration in the material, temperature, and relative humidity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The object of the present invention is a graphite-free friction material for brake pads comprising a specific amount of abrasive; coke; metal sulfides; powdered metals and / or metal alloys and / or intermetallic compounds; aramid and steel fibers; phenolic resins; and fillers selected from calcium hydroxide, friction powder, PTFE and fluorspar (CAF2).

[0019] Surprisingly, it has been found that the absence of graphite in the friction material significantly reduces the "creep groan" phenomenon, making it negligible. A friction material containing the same components in the same ratios but with an increasing amount of graphite exhibits an increasingly severe "creep groan" phenomenon.

[0020] Preferably, the friction material according to the present invention does not contain graphite or graphene.

[0021] The friction material of the present invention advantageously belongs to the class of so-called "NAO" ("non-asbestos organic") materials. The friction material of the present invention preferably belongs to the class of so-called "low steel" materials. The friction material of the present invention preferably belongs to the class of so-called "copper-free" materials. The friction material of the present invention is preferably free or substantially free of asbestos, heavy metals, copper and their alloys.

[0022] The friction material of the present invention contains one or more abrasives in an amount of 20 volume % or more and 30 volume % or less.

[0023] Preferably, the friction material includes one or more abrasives in an amount of 21 vol% to 30 vol%, 22 vol% to 30 vol%, 23 vol% to 30 vol%, 24 vol% to 30 vol%, 25 vol% to 30 vol%, 26 vol% to 30 vol%, 27 vol% to 30 vol%, 28 vol% to 30 vol%, or 29 vol% to 30 vol%.

[0024] In a preferred embodiment, the one or more abrasives are selected from the group consisting of potassium titanate, chromite, magnesium oxide, zinc oxide, aluminum oxide, silicon carbide, and corundum.

[0025] According to this embodiment, the friction material includes at least one of potassium titanate, chromite, magnesium oxide, zinc oxide, aluminum oxide, silicon carbide, and corundum as an abrasive.

[0026] Preferably, the friction material contains potassium titanate, chromite, magnesium oxide, zinc oxide, aluminum oxide, silicon carbide and corundum as abrasives.

[0027] The friction material may or may not contain other abrasives in addition to those mentioned above, for example, selected from zirconium, zirconium silicate, zirconium oxide, mica, talc, kaolin, barium sulfate, calcium carbonate, calcium silicate, iron oxide, and mullite.

[0028] The friction material of the present invention contains coke in an amount of 10 volume % or more and 20 volume % or less.

[0029] Preferably, the friction material includes coke in an amount of 11 vol% to 20 vol%, 12 vol% to 20 vol%, 13 vol% to 20 vol%, 14 vol% to 20 vol%, 15 vol% to 20 vol%, 16 vol% to 20 vol%, 17 vol% to 20 vol%, 18 vol% to 20 vol%, or 19 vol% to 20 vol%.

[0030] In one embodiment of the present invention, the friction material includes coke in an amount of 16% to 18% by volume, or 16% to 17% by volume.

[0031] The friction material of the present invention contains up to 10% by volume of one or more metal sulfides.

[0032] Preferably, the friction material comprises one or more metal sulfides in an amount of 5 vol.% to 10 vol.%, 6 vol.% to 10 vol.%, 7 vol.% to 10 vol.%, 8 vol.% to 10 vol.%, or 9 vol.% to 10 vol.%.

[0033] According to one embodiment, the friction material comprises one or more metal sulfides selected from antimony sulfide (Sb2S3), molybdenum sulfide (MoS2), tungsten sulfide (WS2), tin sulfide (SnS, SnS2), zinc sulfide (ZnS), iron sulfide (FeS), copper sulfide (Cu2S), and mixed sulfides. The term "mixed sulfide" refers to a sulfide of two or more metals. In particular, the term "mixed sulfide" refers to a sulfide of metals having different valences.

[0034] According to one embodiment of the present invention, the one or more metal sulfides are selected from the group consisting of FeS and SnS.

[0035] According to an embodiment of the present invention, the friction material includes at least FeS and SnS.

[0036] The friction material of the present invention comprises up to 20% by volume of one or more metals in powder form and / or metal alloys in powder form and / or intermetallic compounds in powder form.

[0037] Preferably, the friction material comprises one or more metals in powder form and / or metal alloys in powder form and / or intermetallic compounds in powder form in an amount of 5% to 20% by volume, 5% to 15% by volume, 5% to 10% by volume, 6% to 10% by volume, 7% to 10% by volume, 8% to 10% by volume, or 9% to 10% by volume.

[0038] According to different embodiments, the intermetallic compound can be a binary intermetallic compound or a ternary intermetallic compound.

[0039] According to one embodiment of the present invention, the friction material comprises at least one, and preferably both, of zinc in powder form and aluminum in powder form in the volume amounts defined above.

[0040] According to one embodiment of the invention, the friction material comprises zinc in powder form, aluminum in powder form, and at least one intermetallic compound, preferably a ternary intermetallic compound, in powder form, in the volume amounts defined above. The friction material may or may not comprise other metals and / or metal alloys and / or intermetallic compounds in powder form in addition to those defined above.

[0041] In addition to being in powder form, the friction material may also include metals and / or metal alloys and / or intermetallic compounds in fiber form.

[0042] The friction material of the present invention comprises up to 40% by volume of fibrous material including aramid fibers and steel fibers.

[0043] Preferably, the friction material comprises at most 30% by volume, or at most 20% by volume, or at most 10% by volume of said fibrous material. For example, the friction material comprises at least 5% by volume and at most 10% by volume, or at most 6% by volume and at most 10% by volume, or at most 7% by volume and at most 10% by volume, or at most 8% by volume and at most 10% by volume, or at most 9% by volume and at most 10% by volume of said fibrous material.

[0044] According to one embodiment, the fibrous material consists of aramid and steel fibers.

[0045] According to alternative embodiments, the fibrous material may further comprise organic and / or inorganic and / or metal fibers, in addition to the aramid and steel fibers, such as, for example, carbon fibers, acrylic fibers, rock wool, rock fibers, glass fibers, ceramic fibers, mineral fibers, wollastonite, copper fibers, zinc fibers, tin fibers, bronze fibers, brass fibers, iron fibers, etc.

[0046] The friction material of the present invention contains 10-20% by volume of a phenol resin as a binder.

[0047] Preferably, the friction material comprises phenolic resin in an amount of 15% to 20% by volume, 16% to 20% by volume, 17% to 20% by volume, 18% to 20% by volume, or 19% to 20% by volume. Preferably, said friction material consists of said phenolic resin in an amount of 17% to 19% by volume, or 17% to 18% by volume.

[0048] The friction material of the present invention comprises up to 10% by volume of one or more fillers selected from the group consisting of calcium hydroxide, friction powder, PTFE, and fluorite. The expression "friction powder" refers to a powder obtained by crosslinking a liquid derived from cashew shells and then grinding it.

[0049] Preferably, the friction material comprises the one or more fillers in an amount of 5% by volume to 10% by volume, 6% by volume to 10% by volume, 7% by volume to 10% by volume, 8% by volume to 10% by volume, or 9% by volume to 10% by volume.

[0050] According to one embodiment, the friction material includes calcium hydroxide, friction powder, PTFE, and fluorspar as fillers in the aforementioned amounts by volume.

[0051] In a specific embodiment of the present invention, the friction material comprises: 28 to 30 volume percent, preferably about 29 volume percent, of potassium titanate, chromite, magnesium oxide, zinc oxide, aluminum oxide, silicon carbide, and corundum as abrasives; 16 to 18 volume percent, preferably about 17 volume percent, of coke; 8 to 10 vol. %, preferably about 9 vol. %, FeS and SnS; 8 to 10% by volume, preferably about 9% by volume, of powdered zinc, powdered aluminum, and at least one intermetallic compound, preferably powdered, such as the intermetallic compound being ternary; 5 to 10% by volume, preferably about 8% by volume, of a fibrous material consisting of aramid and steel fibers; 17 to 19 volume percent, preferably 17 to 18 volume percent, of a phenolic resin; 8 to 10 volume percent, preferably 9 to 10 volume percent, of calcium hydroxide, friction powder, PTFE and fluorspar as fillers, with the proviso that said composition does not contain graphite.

[0052] The friction material of the present invention is advantageously obtained by homogeneously mixing the above-mentioned components in the amounts specified above.

[0053] A further object of the invention is a pad for a disc brake comprising a friction layer intended to cooperate with a disc of a disc brake, the friction layer being made of a friction material as defined above.

[0054] The friction layer consists of a frictionally active surface intended to cooperate with the disc of a disc brake.

[0055] Preferably, the friction layer comprised in the disc brake pad is obtained through a molding step in a suitable mould. Preferably, the molding step is carried out at a pressure of 1-6 bar, more preferably 2-5 bar, for example about 3 bar. Preferably, the molding step is carried out at a temperature of 120-180°C, more preferably 140-160°C, for example about 150°C. Preferably, the friction layer obtained from the molding step is subjected to a post-hardening by heat treatment at a temperature between 100-300°C for a time between 1-20 hours. Afterwards, if necessary, a second surface heat treatment called "scorching" and any mechanical machining can be performed.

[0056] Preferably, the disc brake pad of the present invention further comprises a base metal plate and a substrate (or underlayer) interposed between the plate and the friction material. Preferably, the friction material, underlayer and plate are molded together using the process described above, thereby obtaining the pad.

[0057] Another object of the invention is a braking system for a disc brake, comprising a disc and a pad as defined above intended to cooperate with said disc.

[0058] experiment

[0059] Friction materials A, B, C, and D were prepared. Friction material A is according to the present invention, and was prepared with the composition shown in Table 1. Friction materials B, C, and D were prepared as comparative examples, and contained an increased amount (volume %) of graphite relative to the volume of the composition of material A. especially, Friction material A does not contain graphite; Friction material B contains graphite in an amount of 3% by volume of the composition of material A; Friction material B contains graphite in an amount of 5% by volume of the composition of material A; Friction material B contains graphite in an amount of 11% by volume of the composition of material A.

[0060] [Table 1]

[0061] Friction material A was evaluated against reference materials B, C and D on a roller stand by varying the level of road gradient (5%, 10%, 15% and 20% both downhill and uphill) and decreasing the pressure ramp starting from the equilibrium condition.

[0062] The tests were carried out according to a test matrix that varied the temperature levels of the brake system (from -20°C to +250°C) and the temperature and humidity conditions in the test room in two stages: - Temperature: 15℃, -30 - Relative humidity: 10%, 90

[0063] Next, each of the friction materials A, B, C, and D was tested under the following test conditions: 1) 15℃, humidity 10% (high temperature drying); 2) 15℃, humidity 90% (hot and humid); 3) -30℃, humidity 10% (low temperature drying); 4) -30℃, humidity 90% (cold and humid).

[0064] The evaluation of friction materials A, B, C, D was carried out by assigning a score of 2-10 (the so-called creep growth score) to the materials tested under the aforementioned temperature and humidity conditions, according to a function that takes into account the intensity and duration of the "creep growth" phenomenon detected. A higher score indicates a reduced "creep growth" phenomenon.

[0065] Table 2 summarizes the creep grout scores obtained for materials A, B, C and D under the four test conditions.

[0066] [Table 2]

[0067] As is clear from the above table, friction material A (according to the present invention) showed the highest score under all test conditions, which indicates that the absence of graphite in the material significantly reduces the "creep growth" phenomenon.

[0068] Comparative materials B, C, and D score poorly under all test conditions, with scores decreasing as the graphite content increases, indicating an increase in the intensity and duration of the "creep hum" phenomenon.

[0069] The effect of graphite content on the test conditions is also shown in the "Main Effects Plot" diagram shown in Figure 1, which relates the average value of the rating ("Average Creep Growing Score") as the control parameters that affect the "Creep Growing" phenomenon, namely graphite content, temperature, and relative humidity, are varied.

[0070] The diagram in Figure 1 shows the deteriorating effect (i.e., score reduction) of low temperature, high relative humidity, and the presence of graphite. Note in particular that the concentration of graphite is the most important factor with respect to the assessment. In fact, changing the concentration from 0 to 11% by volume produces a score change of over 2.5. Also note how gradual the increase in score with decreasing graphite is as a function of concentration.

[0071] It is obvious that what has been described is only one specific embodiment of the invention, and a person skilled in the art can make all the necessary modifications to the materials, pads and braking system to adapt it to his particular conditions, without departing from the scope of protection defined in the appended claims.

Claims

1. 20-30% by volume of one or more abrasive materials; 10-20% by volume of coke; up to 10% by volume of one or more metal sulfides; up to 20% by volume of one or more metals and / or metal alloys and / or intermetallic compounds in powder form; up to 40% by volume of fibrous material including aramid fibers and steel fibers; 10 to 20% by volume of a phenolic resin as a binder; up to 10% by volume of one or more fillers selected from calcium hydroxide, friction powder, PTFE, and fluorite; Graphite-free friction material.

2. 2. The friction material of claim 1, wherein the one or more abrasives are selected from the group consisting of potassium titanate, chromite, magnesium oxide, zinc oxide, aluminum oxide, silicon carbide, and corundum as abrasives.

3. 3. The friction material according to claim 1, comprising potassium titanate, chromite, magnesium oxide, zinc oxide, aluminum oxide, silicon carbide, and corundum as abrasives.

4. 3. The friction material according to claim 1, comprising the one or more abrasives in an amount of 25% by volume or more and 30% by volume or less, preferably 28% by volume or more and 30% by volume or less.

5. 3. The friction material according to claim 1, comprising coke in an amount of 15% by volume or more and 20% by volume or less, preferably 16% by volume or more and 18% by volume or less.

6. 3. The friction material according to claim 1, comprising 5% by volume or more and 10% by volume or less, preferably 8% by volume or more and 10% by volume or less, of one or more metal sulfides.

7. 3. The friction material according to claim 1, wherein the one or more metal sulfides are selected from FeS and SnS.

8. 3. The friction material according to claim 1, wherein the one or more metals and / or metal alloys and / or intermetallic compounds are contained in a powder form in an amount of 5% by volume or more and 10% by volume or less, preferably 8% by volume or more and 10% by volume or less.

9. Zinc in powder form, Aluminum in powder form, and 3. The friction material according to claim 1 or 2, comprising at least one intermetallic compound, preferably a ternary intermetallic compound, in powder form.

10. 3. The friction material according to claim 1 or 2, comprising at most 30% by volume, preferably at most 20% by volume, more preferably at most 10% by volume of said fibrous material.

11. 3. The friction material according to claim 1, wherein the fibrous material comprises aramid fibers and steel fibers.

12. 3. The friction material according to claim 1, wherein the phenolic resin is contained in an amount of 15% by volume or more and 20% by volume or less, preferably 17% by volume or more and 19% by volume or less.

13. 3. The friction material according to claim 1, wherein the one or more fillers comprise 5-10% by volume, preferably 8-10% by volume.

14. 28% to 30% by volume of an abrasive material, the abrasive material including potassium titanate, chromite, magnesium oxide, zinc oxide, aluminum oxide, silicon carbide, and corundum; 16-18 vol. %, preferably about 17 vol. % coke; 8-10% by volume, preferably about 9% by volume, of FeS and SnS; 8-10% by volume, preferably about 9% by volume, of powdered zinc, powdered aluminum, and at least one intermetallic compound, preferably in powder form; a fibrous material consisting of 5-10% by volume, preferably about 8% by volume, aramid fibers and steel fibers; 17-19% by volume, preferably 17 to 18% by volume, of a phenolic resin; As fillers, 8 to 10% by volume, preferably 9 to 10% by volume of calcium hydroxide, friction powder, PTFE and fluorite are included; 3. The friction material according to claim 1, which does not contain graphite.

15. Pad for a disc brake, comprising a friction layer intended to cooperate with a disc of a disc brake, characterized in that said friction layer is made of a friction material according to claim 1 or 2.

16. 3. A braking system for a disc brake comprising a disc and a pad consisting of a friction layer intended to cooperate with said disc, characterized in that said friction layer is made from the friction material according to claim 1 or 2.

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