Braking device for motor vehicles and production method thereof

Abstract

The present invention concerns a braking device and a method for its production. The device comprises a metallic support element (10), a block of friction material attached to one side of the metallic support element and at least one sensor with an associated electrical circuit formed on the metallic support element and interposed between it and the block of friction material. The metallic support element (10) comprises a glass enamel coating (12) having an amorphous or partially crystalline structure which forms, altogether, a corrosion protection layer of the metallic support element (10) and, locally, also an intermediate thermal and electrical insulation layer between said side of the metallic support element (10) bearing the block of friction material and said sensor with its associated electrical circuit.

Description

[0001] “BRAKING DEVICE FOR MOTOR VEHICLES AND PRODUCTION METHOD

[0002] THEREOF”

[0003] DESCRIPTION

[0004] Technical Field

[0005] The present invention generally relates to the field of braking devices for motor vehicles, and in particular concerns a braking device and a method for its production.

[0006] Background Art

[0007] From published patent application US 20210348666 Al there is known a braking device for motor vehicles which comprises a block of friction material fixed to a metallic support element and one or more piezoelectric sensors also fixed to the metallic support element and interposed between the metallic support element and the block of friction material. During braking of the vehicle, the piezoelectric sensors are deformed by the forces exchanged between the block of friction material and the element to be braked which is integral with the wheel of the vehicle, and generate an electrical signal which is transmitted to a processing unit via a galvanically insulated electrical circuit which is fabricated directly on the metallic support element. A layer of heat-insulating material is interposed between the electrical circuit and the metallic support element in order to reduce the thermal stress on the electrical circuit and the sensors.

[0008] This known braking device is fabricated by initially applying a thermally insulating layer to the metallic support element. Subsequently, the galvanically insulated electric circuit is integrated on the metallic support element. For this purpose, a first screen-printed layer of electrically insulating material is initially deposited on the thermally insulating layer. Subsequently, a layer of electrically conductive material defining the electrical circuit is deposited on this first screen-printed layer. Finally, a second layer of electrically insulating material, which leaves the contact areas uncovered for the electrical connection of the piezoelectric sensors, is deposited on the layer of electrically conductive material.

[0009] Thermal Barrier Coating (TBC) materials, yttrium-stabilized zirconia or magnesium stabilized zirconia, ceramic compounds or special paints are generally used to form the thermally insulating layer. The electrically insulating layers typically consist of a base of alumina and graphite particles immersed in a polymer matrix. The electrically conductive layer consists of silver- or palladium-based screen-printing pastes.

[0010] After the electrical circuit is formed, the electrodes of the piezoelectric sensors are welded to the corresponding contact areas of the electrical circuit and then coated with a protective element. Finally, the friction material block of the braking device is formed on the electric circuit and the piezoelectric sensors by hot pressing.

[0011] A feature of this well-known braking device is that the thermal and electrical insulation between the electrical circuit of the sensors and the metallic support metal element is obtained by applying to the latter overlapping layers of insulating materials with different physical and chemical characteristics, each of which separately performs the function of thermal insulation and electrical insulation. However, from an operational and implementation point of view, applying these insulating layers in sequence onto the metallic support metal element is an expensive and timeconsuming operation.

[0012] Moreover, the insulating layers, because of how they are made, do not contribute, either individually or in combination, to the protection of the metallic support element against corrosion caused by weathering and other aggressive media. Instead, the corrosion protection relies upon a specific coating of the metallic support element which is applied with an epoxy-based paint or by electroplating with chromium, zinc or zinc / nickel alloys using galvanic treatments.

[0013] Epoxy coating is a method commonly used to protect the metallic support element of a braking device of the above-mentioned type from corrosion. Epoxy paints are a broad category of coating products that have as their unifying characteristic the use of a binder consisting of epoxy resins. Indeed, like all paints, they consist of a mixture of chemical products which, when applied to an object, forms a thin, mechanically resistant coating on its external surface, capable of preserving the object from the aggression of chemical and physical agents. Epoxy paints can also modify and improve the appearance of the treated object by providing coloration, smoothness and gloss. Despite these advantages, epoxy resin paints have a major drawback when applied to braking devices. During braking, especially with a heavy and / or fast-moving vehicle, the frictional resistance exerted by the friction block can generate temperatures of up to 600 °C in the friction material. The generated heat is transferred to the metallic support element of the braking device, causing the epoxy paint to progressively degrade. When the epoxy paint has deteriorated to the point that it is no longer able to protect the metallic support element from corrosion, this element rusts inexorably.

[0014] Galvanization is another method traditionally used to protect the surface of the metallic support element of the braking device from corrosion. Patent publication US 5 161 654 describes a braking device comprising a block of friction material attached to a metallic support metal element, wherein before the block of friction material is pressed onto the metallic support element, a galvanized metal coating consisting of copper, silver, tin, zinc, cadmium or chromium is applied to the metallic support element. A major disadvantage of braking devices of this type is that the metals forming the galvanized metal coating are progressively released into the environment during both use and the recovery and disposal of the braking devices, and due to the toxicity of these metals, they pose an environmental and health hazard.

[0015] Summary of Invention

[0016] It is an object of the present invention to overcome the drawbacks of a braking device for motor vehicles according to the known prior art. Within the scope of this object, an aim of the invention is to provide a braking device having a high degree of resistance to elevated temperatures and the most common corrosive agents, such as moisture, salt, chemicals, lubricants and fuel oils, together with a greater environmental compatibility.

[0017] A further object of the invention is to provide a braking device in which the corrosion protection coating of the metallic support element can also serve as a thermally and electrically insulating coating between the metallic support element and the sensors with the associated electrical connection circuits, thereby obviating the necessity of applying layers of different materials on the metallic support element to separately perform the functions of corrosion protection, thermal insulation and electrical insulation, respectively.

[0018] Still another object of the invention is to provide a braking device that is easily industrialized and inexpensive to manufacture.

[0019] According to the invention, these and other objects are achieved by a braking device with the features of claim 1.

[0020] The glass enamel coating on the metallic support element not only imparts to the latter superior corrosion resistance characteristics, but also forms an electrically insulating layer, which allows the integration of sensors and their electrical circuits, as well as a thermally insulating layer, which reduces the transmission of heat between the metallic support element and the sensors and their electrical connection circuits. This obviates the necessity of applying overlapping layers of dissimilar materials on the metallic support element in order to separately perform the functions of corrosion protection, thermal insulation and electrical insulation, respectively. Instead, in the present invention the glass enamel coating applied to the metallic support element performs all three of these functions individually and simultaneously. This allows to simplify the operations and reduce the cost of manufacturing the braking device.

[0021] The composition of the glass enamel of the coating is chosen so that it chemically adheres to the surface of the metallic support element. To this end, the composition of the glass enamel may include various glass-forming metal oxides and metal adhesion promoters. These oxides may include, but are not limited to, SiCh, AI2O3, B2O3, ZnO, BaO, Bi2C>3, TiCh, ZrCh, Na20, K2O, CaO, MgO, CO2O3, NiO, MnCh, Fe2O3, CuO, V2O3, MoO and &2O3.

[0022] The specific composition of the glass enamel varies depending on the metal material of the support element to be coated. The metallic support element can be made of steel, cast iron or aluminium. Depending on the material used, the composition of the glass enamel is chosen to enable stable adhesion to the surface of the metallic support element.

[0023] The shape of the metallic support element can be flat or curved, depending on the type of braking device. The surface of the metallic support element facing the block of friction material may be structured with different elements, such as localized protrusions, holes, rivets, pins, fastening hooks, spikes or barbs.

[0024] The glass enamel coating may cover the entire or part of the surface of the metallic support element, depending on the type of metallic support element used. In fact, it may be necessary not to cover certain areas of the metallic support element with glass enamel to allow the application of elements such as weld studs or rivets.

[0025] The glass enamel can be applied to the surface of the metallic support element by using known techniques, for example by powder coating or wet enameling. In order to permanently bond the applied glass enamel to the metallic support element, this is subjected to heating up to 800- 900°C to form a uniform and compact glass layer on the surface of the metallic support element. During the heating operation, the glass layer protects the surface of the metallic support element from oxidation at elevated temperatures. After cooling, the glass enamel forms an extremely durable coating that protects the metallic support element from the most common corrosive agents, such as moisture, chemicals, salt, lubricants and fuel oils.

[0026] Brief Description of Drawings

[0027] The braking device according to the present invention will now be described in more detail with reference to some of its preferred, and non-limiting, embodiments illustrated in the accompanying drawings, in which:

[0028] Figures 1 and 2 show some examples of a first type of metallic support element of a braking device according to the invention,

[0029] Figures 3 and 4 show some examples of a second type of metallic support element of a braking device according to the invention, and

[0030] Figure 5 shows a detail of a glass enamel coating on a metallic support element of a braking device according to the invention.

[0031] Detailed Description of Preferred Embodiments of the Invention

[0032] Braking devices for motor vehicles to which the invention is applied may be of the type equipped with a brake pad or of the type equipped with a brake block type. In the first type, the metallic support element of the block of friction material is configured as a flat plate, as illustrated in Figs. 1 and 2, while in the second type, the metallic support element of the block of friction material is configured as a curved, roughly semicircular plate, as illustrated in Figs. 3 and 4. Regardless of the shape of the metallic support element, the braking device according to the invention comprises a glass enamel coating having an amorphous or partially crystalline structure that covers the entire or part of the surface of the metallic support element. The term ‘partially crystalline’ as used herein means that the glass enamel coating may contain one or more crystalline phases in an amorphous or non-crystalline matrix. Fig. 5 schematically and partially illustrates a metallic support element according to the invention, generally denoted by 10 and having a metallic body 11 and a glass enamel coating 12. The glass enamel coating 12 may be formed as a single layer, but a two-layer coating is preferable, as shown in Fig. 5, with a base layer 12A, which promotes the adhesion of the glass enamel coating 12 to the body 11 of the metallic support element 10, and a cover layer 12B, which is suitable for imparting specific characteristics to the metallic support element 10 in relation to both the intended use and the appearance of the object.

[0033] The metallic material of the support element 10 may be steel, cast iron or aluminium. The chemical composition of the glass enamel is specially formulated to adhere firmly to the surface of the metallic support element without leaving defects, such as crevices, bubbles, pinholes or cracks. To this end, the composition of glass enamel may include various glass-forming metal oxides and metal adhesion promoters. These oxides may include, but are not limited to, SiCh, AI2O3, B2O3, ZnO, BaO, Bi2C>3, TiCh, ZrCh, Na2O, K2O, CaO, MgO, CO2O3, NiO, MnCh, Fe2C>3, CuO, V2O3, MoO and CT2O3. The specific composition of the glass enamel varies depending on the metallic material of the support element to be coated.

[0034] The surface of the metallic support element 10 that faces the block of friction material may be flat, as shown in Fig. 1, or structured, as shown in Fig. 2. In the latter case, the surface of the metallic support element 10 facing the block of friction material may be structured with various elements, such as localized protrusions, holes, rivets, pins, prongs, fastening hooks or barbs, as described in patent publication US 9 388 872 Bl, which are made by mechanical methods known in the art.

[0035] The metallic support element 10 may be entirely covered by the glass enamel coating, or it may be partially covered, leaving some empty areas to allow for subsequent operations, e.g., the welding of pins on the surface of the metallic support element facing the block of friction material.

[0036] The glass enamel coating can be applied using known techniques, such as powder coating or wet enameling. After application, the glass enamel is subjected to a heating operation at a temperature of between 800 °C and 900 °C in order to allow the glass material to melt and promote its adhesion to the surface of the metallic support element 10. As mentioned above, the coating 12 may comprise a single layer, but preferably it comprises two layers, namely a base layer (ground coat) 12 A, which promotes adhesion of the coating to the surface of the metallic support member, and a cover layer (cover coat) 12B, which is adapted to impart specific characteristics to the metallic support member 10, depending on the uses and appearance of the object.

[0037] After cooling, the glass enamel forms a continuous coating that is resistant to elevated temperatures and chemical attack. The glass enamel coating also forms an electrically insulating layer on which the electrical circuits for the brake device sensors can be fabricated using, for example, thick film screen-printing techniques. In addition, the sensors of the braking device can also be integrated directly onto the glass enamel coating using, for example, known positioning and fixing techniques.

[0038] Examples of Invention

[0039] Some examples of the realization of the invention will be described hereinafter:

[0040] In this example, the surface of the metallic support element is flat with no protrusions. In this case, the enamel is applied in the form of an electrostatic powder over the entire surface of the metallic support element. Subsequently, the metallic support element is fired to allow the glass powder to melt and the melted enamel to adhere to the surface of the metallic support element.

[0041] In this example, the surface of the metallic support element is structured with localized protrusions. The shape and number of protrusions depend on the particular design of the metallic support element manufacturer and the intended use. The protrusions are usually obtained by cold or hot forming of the metallic support element, if it is made of steel or aluminium, or by die-casting, if it is made of cast iron. The enamel, in the form of electrostatic powder, is applied to the entire surface of the metallic support element. Subsequently, the metallic support element is fired to allow the glass powder to melt and the molten enamel to adhere to the surface of the metallic support element.

[0042] Ill

[0043] In this example, the surface of the metallic support element is structured with holes which pass through the body of the metallic support element. The size and number of the holes depend on the particular design of the metallic support element manufacturer and the intended use. The holes are usually obtained by cold or hot punching of the metallic support element. These holes are usually made in support elements made of steel, while they are not present in those made of cast iron or aluminium due to lack of mechanical strength. Enamel, in the form of an electrostatic powder, is applied to the entire surface of the metallic support element. Subsequently, the metallic support element is fired to allow the glass powder to melt and the molten enamel to adhere to the surface of the metallic support element.

[0044] Example IV

[0045] In this example, the surface of the metallic support element is structured with rivets. A rivet is a permanent mechanical fastener and consists of a smooth cylindrical shaft with a head at one end. When applied to a brake pad, the rivet acts as a fastener for the friction material. During installation, the rivet is inserted into a corresponding hole drilled in the metallic support element, then the distal end from the head is riveted, creating a second head. In this case, the application of enamel powder and the subsequent firing operation must be carried out before installing the rivets.

[0046] Example V

[0047] In this example, the surface of the metallic support element is structured with pins. A pin is a cylindrical fastener applied to a metal substrate, usually through material connection methods such as arc welding. Enamel powder is applied to the surface of the metallic support element, except for areas where the pin is to be welded. These uncoated areas can be achieved by applying a polymeric material, such as a paste or adhesive tape, prior to the application of the enamel powder. To allow the welding process to take place, the uncoated areas must be free of contaminants, such as traces of enamel or polymer, or oxidation induced by the firing operation. Since contamination is difficult to avoid, especially in large series production, it is necessary to clean the welding area with processes such as grinding, milling or sandblasting. Example VI

[0048] In this example, the surface of the metallic support element is structured with spikes or hooks, obtained by known mechanical methods. Enamel is applied in the form of an electrostatic powder over the entire surface of the metallic support element. Subsequently, the metallic support element is fired to allow the glass powder to melt and the melted enamel to adhere to the surface of the metallic support element.

[0049] It is clear from the above that the invention achieves its intended purposes. In particular, the glass enamel coating for corrosion protection of the metallic support element of the braking device according to the invention is also capable of acting as a thermally and electrically insulating coating between the metallic support element and the sensors and the related electrical connection circuit, thereby obviating the necessity of applying layers of different materials on the metallic support element to separately perform the functions of corrosion protection, thermal insulation and electrical insulation, respectively. The glass enamel coating, therefore, not only provides high resistance to elevated temperatures and the most common corrosive agents, such as moisture, salt, chemicals, lubricants and fuel oils, but also serves as a suitable substrate for the integration of sensors and related electrical circuits of a braking device. The invention thus conceived is easily industrialized and inexpensive to implement.

Claims

CLAIMS1. A braking device for motor vehicles, comprising a metallic support element (10), a block of friction material attached to one side of the metallic support element and at least one sensor with an associated electrical circuit formed on the metallic support element and interposed between it and the block of friction material, characterized in that the surface of said metallic support element (10) comprises a glass enamel coating (12) having an amorphous or partially crystalline structure which forms, altogether, a corrosion protection layer of said metallic support element (10) and, locally, also an intermediate thermal and electrical insulation layer between said side of the metallic support element (10) bearing the block of friction material and said sensor with its associated electrical circuit.

2. A braking device according to claim 1, characterized in that said metallic support element (10) is made of steel, cast iron or aluminium.

3. Braking device according to claim 1, characterized in that said glass enamel comprises glassforming and metal adhesion-promoting metal oxides.

4. Braking device according to claim 3, characterized in that said glass enamel includes one or more metal oxides chosen from SiC , AI2O3, B2O3, ZnO, BaO, Bi2C>3, TiCh, ZrCh, Na2O, K2O, CaO, MgO, CO2O3, NiO, MnC , Fe2O3, CuO, V2O3, MoO and Cr2O3.

5. Braking device according to claim 1, characterized in that said metallic support element has a flat or curved shape.

6. Braking device according to claim 1 , characterized in that the surface of the metallic support element (10) facing the block of friction material is structured with localized protrusions, holes, rivets, pins, fastening hooks, spikes, or barbs.

7. Braking device according to claim 1, characterized in that the glass enamel coating is applied to the whole, or a portion only, of the surface of the metallic support element (10).

8. Braking device according to claim 1, characterized in that the glass enamel coating of the metallic support element (10) forms a substrate suitable for allowing the integration of sensors and related electrical circuits.

9. A braking device according to claim 1, characterized in that the glass enamel coating of the metallic support element (10) comprises a single layer or preferably two layers, wherein a base layer promotes the adhesion of the coating to the surface of the metallic support element (10), and a cover layer imparts specific characteristics to the metallic support element (10).

10. A method for producing a braking device according to one or more of the preceding claims, characterized in that the metallic support element (10) is subjected to a pre-treatment step to promote the adhesion of the glass enamel coating layer, at least one powder or wet enameling step, at least one controlled heating step at a temperature between 800 °C and 900 °C for a predetermined time, and at least one controlled cooling step.

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