Patent Description:
Such safety fuses are currently known and are used to protect an electrical circuit from an overcurrent.

One type of fuse currently known and used in motor vehicles is the so-called MIDI fuse, an example of which is illustrated in the assembled condition in <FIG>.

This fuse has a first contact metal portion, a second contact metal portion, and a melting section connecting the first contact portion with the second contact portion to form a single metal part. The first contact portion, the second contact portion, and the melting section lie on a common plane.

The melting section is enclosed by a casing made of a non-conductive material, preferably polymeric material. At least part of the first contact portion and at least part of the second contact portion freely protrude from the casing along the same direction in respective opposite directions.

The casing protrudes with respect to the common plane on both sides of the plane, for about the same distance from the plane on both sides. The casing consists of two hollow half-shells provided with removable mutual coupling means. Each half-shell then has an inner surface facing the melting section and an outer surface facing outside the fuse.

The mutual contact edges of the two half-shells have complementary shapes for a shape coupling in a closed condition, and the removable reciprocal coupling means typically comprise one or more pins adapted to penetrate into corresponding holes or alternatively holes with rivets.

The fuse also generally provides a hole in the part of the first contact portion protruding from the casing, which hole allows the fixing of the fuse, by means of a screw or the like, to a special support outside the fuse. Two holes may be provided, each on a contact portion, or no holes may be provided.

When an overcurrent occurs which exceeds the amperometric flow rate of the fuse, the melting section melts, causing the circuit to open, securing the electrical devices connected to the circuit and the entire vehicle.

However, it is possible that between the two contact portions, once separated from the melting of the intermediate section, an electric arc develops. This phenomenon effectively closes the circuit and can generate a situation of great danger. Experimental evidence suggests that during the melting of the intermediate section, some of the metal material sublimates, creating a dispersion of dust inside the casing. Such metallic-based dust dispersion inside the casing would be sufficient to promote the occurrence of the electric arc phenomenon between the two fuse ends.

A similar phenomenon is taken into account by document <CIT>, which detects how sparks created by the sublimation of the melting section can deposit particles on the inner surface of the casing. If these particles are arranged to be electrically connected together, they may reduce the effectiveness of the fuse. The document therefore discloses a fuse with inserts provided on the inner surface of the two half-shells, which inserts are provided with hemispherical protrusions projecting in the direction of the melting section. The presence of said protrusions increases the particle deposition surface and thus minimizes the likelihood that the particles can be electrically connected to each other.

However, this solution does not take into account the suspended dust particles, and the mere presence of hemispherical protrusions, designed to increase the area of the inner surface of the casing, leaves the open space inside the casing substantially unchanged and does not sufficiently limit the movements and possible electrical connections between such suspended particles. This results in reduced performance, which does not guarantee a satisfactory minimization of the risk of the electric arc occurrence. The publication <CIT> describes a safety fuse for use in a motor vehicle according to the preamble of claim <NUM>.

There is therefore currently an unmet need by the state-of-the-art fuses to eliminate or at least significantly reduce the possibility of electric arcs occurring between the fuse ends after melting.

The present invention seeks to overcome these drawbacks of the currently known fuses with a simple and inexpensive solution.

The present invention achieves such objects with a safety fuse for use in a motor vehicle, as set forth in claim <NUM>. Further embodiments are inter alia disclosed in the dependent claims.

The alveolar structure divides the inner space of the casing surrounding the melting section into separate subspaces, so that after melting, the metal-based dust cannot freely disperse throughout the inner space of the casing, but remains confined in cells separate from each other. This technical effect significantly reduces the possibility of triggering an electric arc between the fuse ends.

In one embodiment the alveolar structure is provided only in the half-shell portion facing the melting section.

According to the invention, the first contact portion, the second contact portion and the melting section lie on a common plane and said walls are perpendicular to said common plane.

According to the invention, the top edges of said walls define a surface of the alveolar structure, which surface of the alveolar structure is flat and parallel to said common plane. Top edge of the wall is intended as the edge of the wall which is not constrained to the inner surface of the half-shell.

In a further embodiment, in the assembled condition of the fuse, said surface of the alveolar structure is closer to the melting section than to the inner surface of the respective half-shell.

In one embodiment, the walls are arranged perpendicular to each other and form rectangular-base cells.

According to an improvement, the walls form square-base cells.

In a preferred embodiment, the walls are made of non-conductive material.

According to the invention, the walls forming the alveolar structure are integrally formed with the related half-shell, preferably by moulding, for example injection moulding.

In one embodiment, the melting section is shaped according to a loop and the casing in the assembled condition of the two half-shells has an intermediate wall, which intermediate wall is positioned inside said loop and is connected to both half-shells.

The intermediate wall helps to increase the insulation between the fuse ends after melting, helping to avoid the occurrence of the electric arc.

According to one embodiment, said intermediate wall is integrally formed with one of the two half-shells.

In a further embodiment, at least part of the first contact portion and at least part of the second contact portion freely protrude from the casing in respective opposite directions along a common straight direction, said intermediate wall provided being arranged perpendicular to said straight direction in the assembled condition of the casing.

In this manner, the intermediate wall is placed transverse to the direction which joins the two fuse ends and acts as a non-conductive barrier.

Experimental tests have shown that the insulation exhibited upon melting acquires a significant increase for the fuses object of the present invention.

In particular, in the event of an insulation greater than <NUM> MOhm required by the current standards of automotive manufacturers, the tested fuses provided with an alveolar structure and an intermediate wall have revealed an insulation well above the requirements.

Repeated test results on a significant plurality of fuses with and without alveolar structure confirmed that all the fuses with alveolar structure always exhibited an insulation greater than <NUM> MOhm.

These tests confirm that the presence of the alveolar structure confers a significant increase in the insulation guaranteed by the fuse.

These and other features and advantages of the present invention will become clearer from the following description of some non-limiting exemplary embodiments illustrated in the attached drawings in which:.

An embodiment example is illustrated in the figures of the safety fuse for use in a motor vehicle according to the present invention.

The fuse comprises a conductive metal part <NUM> consisting of joining a first contact metal portion <NUM>, a second contact metal portion <NUM> and a melting metal section <NUM> connecting the first contact portion <NUM> with the second contact portion <NUM>. The contact portions <NUM> and <NUM> are plate-like. The first contact portion <NUM>, the melting section <NUM> and the second contact portion <NUM> lie on a common plane, and the metal portion <NUM> therefore consists of a flat and suitably shaped metal plate. The shape is such that the melting section <NUM> is shaped according to a loop. The metal part <NUM> may be of any metal material suitable for use in a safety fuse, preferably it consists of tinned copper.

However, other geometries may also be provided, for example the contact portions <NUM> and <NUM> may also not lie on a common plane.

The melting section <NUM> is enclosed by a casing <NUM> made of a non-conductive material. Any non-conductive material suitable for use to enclose the melting section <NUM> of the fuse may be used, for example a polymer. Preferably, the non-conductive material is a glass fibre reinforced polyamide, in particular with a glass fibre content between <NUM> and <NUM>%.

The first contact portion <NUM> and the second contact portion <NUM> freely protrude from the casing <NUM> in respective opposite directions along a common straight direction. It is possible that the contact portions <NUM> and <NUM> completely protrude from the casing <NUM> or alternatively that the contact portions <NUM> and <NUM> only partially protrude from the casing <NUM>. An alternative configuration may also be provided in which the contact portions do not protrude in opposite directions of the same straight direction, but for example form an angle, a U-shaped configuration, an S-shaped configuration in which the contact portions protrude in opposite directions perpendicular to the longitudinal axis of the melting section <NUM>, or the like.

The casing <NUM> consists of a first hollow half-shell <NUM> and a second hollow half-shell <NUM>. Each half-shell <NUM> and <NUM> has an inner surface facing the melting section <NUM> and an outer surface facing outside the fuse.

In the preferred embodiment illustrated in the figures, the two half-shells <NUM> and <NUM> have respective mutual contact edges which have complementary shapes for a shape coupling in the closed condition of the casing <NUM>.

The two half-shells <NUM> and <NUM> are also provided with removable mutual coupling means comprising two first pins <NUM> and two second pins <NUM> provided on the inner surfaces of the first half-shell <NUM> and the second half-shell <NUM>, respectively, which pins <NUM> and <NUM> each extend in the direction of the opposite half-shell.

The first half-shell <NUM> is provided with two first housing holes <NUM> of the second pins <NUM>, while the second half-shell <NUM> is provided with two second housing holes <NUM> of the first pin <NUM>, such that in the coupled condition of the two half-shells <NUM> and <NUM> each pin penetrates the corresponding hole provided on the opposite half-shell. This keeps the two half-shells <NUM> and <NUM> coupled in the closed condition of the casing <NUM>.

The metal part <NUM> is provided with four holes <NUM> in which the pins <NUM> and <NUM> are inserted into the coupling of the two half-shells <NUM> and <NUM>. Therefore, in the assembled condition the fuse has the metal part <NUM> and the casing <NUM> locked in the operating position thereof.

Although the embodiment presented is the preferred embodiment, it is still possible to provide for mutual coupling means of the two half-shells <NUM> and <NUM> which cannot be removed, in which the fuse, once assembled, can no longer be broken down into the constituent components thereof.

The half-shells <NUM> and <NUM> are provided on the inner surface of an open-cell alveolar structure <NUM>, which cells <NUM> in the assembled condition of the fuse expose the opening thereof in the direction of the melting section <NUM>.

In the preferred embodiment illustrated in the figures, both half-shells <NUM> and <NUM> are provided in the inner surface of the alveolar structure <NUM>. However, it is possible to provide the alveolar structure <NUM> only on one half-shell. The alveolar structure <NUM> may also be provided on the entire inner surface or on at least part thereof. If the casing also covers part of the contact portions, the alveolar structure <NUM> is advantageously provided only at the melting section <NUM>. The melting section <NUM> is covered on both sides and substantially in the entirety thereof by the alveolar structures <NUM> of the two half-shells <NUM> and <NUM> in the coupled condition.

The alveolar structure <NUM> consists of a plurality of walls <NUM> protruding from the inner surface of the respective half-shell <NUM> or <NUM>, which walls <NUM> are intersected with each other to form said cells <NUM> open in the direction of the metal part <NUM> in the assembled condition of the fuse. In the embodiment of the figures, the walls <NUM> are positioned perpendicular to the common plane on which the metal part <NUM> lies and are arranged perpendicular to each other to form rectangular-base cells <NUM>, in particular square-base cells <NUM>. However, it is possible to envisage an alveolar structure <NUM> with other geometries, for example with rhomboidal or hexagonal cells, without departing from the objects of the present invention.

The top edges of the walls forming the alveolar structure <NUM> define a surface of the alveolar structure <NUM> itself. Such surface of the alveolar structure <NUM> is flat and parallel to the common plane on which the metal part <NUM> lies, and is closer to the melting section <NUM> than to the inner surface of the respective half-shell <NUM> or <NUM>.

The walls <NUM> forming the alveolar structure <NUM> are integrally formed with the related half-shell <NUM> or <NUM>, preferably by moulding, for example injection moulding. The walls <NUM> are thus made of the same non-conductive material which forms the casing <NUM>. It is optionally possible to provide an alveolar structure <NUM> consisting of an independent element, of non-conductive material, which can be inserted inside the casing <NUM>.

The alveolar structure <NUM> of the first half-shell <NUM> is divided into two parts separated from each other, to form in the centre a housing compartment in which an intermediate wall <NUM> integrally formed with the second half-shell <NUM> is positioned, in the assembled condition of the fuse.

In the assembled condition of the fuse, the intermediate wall <NUM> is positioned inside the loop formed by the melting section <NUM> and is provided perpendicular to the straight direction along which the two contact portions <NUM> and <NUM> protrude from the casing <NUM>.

Claim 1:
A safety fuse for use in a motor vehicle, which fuse comprises a first contact metal portion (<NUM>), a second contact metal portion (<NUM>) and a melting metal section (<NUM>) connecting the first contact portion (<NUM>) with the second contact portion (<NUM>), the melting section (<NUM>) being enclosed by a casing (<NUM>) consisting of a non-conductive material, which casing (<NUM>) consisting of two hollow half-shells (<NUM>, <NUM>) provided with mutual coupling means, each half-shell (<NUM>, <NUM>) having an inner surface facing the melting section (<NUM>) and an outer surface facing outside the fuse,
wherein at least one said half-shell (<NUM>, <NUM>) is provided on at least part of the inner surface of an open-cell alveolar structure (<NUM>) facing the melting section (<NUM>), which cells are open in the direction of the melting section (<NUM>), characterised in that
the alveolar structure is composed of a plurality of walls (<NUM>) integrally formed with the related half-shell and protruding from said inner surface and intersected with each other,
wherein the first contact portion (<NUM>), the second contact portion (<NUM>) and the melting section (<NUM>) lie on a common plane and said walls (<NUM>) are perpendicular to the said common plane, and the top edges of said walls define a surface of the alveolar structure, which surface of the alveolar structure is flat and parallel to said common plane.