FIELD OF THE INVENTION

The present invention relates to the technical sector of shock absorbers for motor vehicles, known as "crash boxes".

DESCRIPTION OF THE PRIOR ART

As known, crash boxes are usually interposed between the front strut of a motor vehicle and the relative front cross beam, and in some cases, the crash boxes are also fixed to the rear cross beams.

Crash boxes comprise a deforming body configured such as to deform when subjected to a compressive stress of a certain entity, for example, an impact; the function of the crash box is such that, for so-called "low speed" impacts, the kinetic energy at the moment of impact is converted into deformation energy of the crash box in order to safeguard the integrity of the vehicle structure.

The state of the art comprises a shock absorber for motor vehicles in which the deforming body is provided with two opposite portions that are also fixed to one another, identifying a tubular member having an elongate development and exhibiting a plurality of intersecting walls that together identify corresponding edges; each portion comprises a half-shell and two-mounting tabs disposed respectively at the ends of the half-shell; at least a portion may be provided with at least a bead which extends along a perpendicular path to the longitudinal axis of the tubular member, which bead is shaped such as to guide the plastic deformation of the deforming body and to regulate the amount of energy required in order to produce a certain degree of deformation of the deforming body as a result of an impact.

Each portion can be obtained by bending (or also by pressing) of a strip of sheet metal to obtain five walls, of which two are end walls, aligned with each other, i.e. lying on a same plane, conforming two fixing tabs, while the remaining three internal walls are angled with respect to one another such as -to-form-a-geometrie-figurerfor-examplera-square-or-a-hexago n-when-the two- above-mentioned portions are fixed to one another at the mounting tabs. The tubular member that is obtained can for example conform a hexagonal cell formed by six interior walls, i.e. three inner walls for each portion, and lateral projections each constituted by two fixing tabs, opposite and joined together for example by spot welding.

The walls are flat. Each portion, in general, can conform a plurality of half- shells, so that the tubular member can be formed by a plurality of flanked hexagonal cells, for example.

The bead is a kind of channel, having a concavity of a given depth, obtainable by deep-drawing compression of the sheet.

The crash box is installed in the motor vehicle in such a way that the longitudinal axis of the tubular member coincides with the deformation direction in the event of a frontal impact.

The beads may be provided in a given number, flanked and parallel to each other, on the walls of the tubular member; these beads also develop up to reaching the entire width of the wall on which they are integrated.

As is known, the efficiency of a crash box depends on the ratio between the mean force required to achieve a certain degree of crushing in the deformation direction and the maximum force absorbed during the crushing phase; the closer this ratio is to being unitary, the more efficient the crash box.

The use of beads has been shown to render an improvement in the efficiency of the crash box.

SUMMARY OF THE INVENTION

The aim of the present invention consists in devising a new-concept crash box having optimum efficiency.

This aim has been attained with the crash box according to claim 1.

In the tract of the bead that is at the edge, advantageously no accumulation, interference or co-penetration of material of the deforming body occurs during the crushing of the crash box; in fact, the bead varies its orientation at the corner, between projecting and retracting. An accumulation, interference or copenetration of material of the deforming body would occur, however, if the bead did not vary the orientation thereof, remaining projecting or retracted. The crushing of the crash box therefore proceeds with an ordered deformation, that is to say with an accordion-like deformation; in this way, the crash box reacts to the crushing with a less fluctuating and therefore more constant force, which maximizes the efficiency of the crash box.

In addition, the deformation of the material of the deforming body occurs in a predictable manner in the section of the bead that is located at the edge: this enables a more accurate calculation of the deformation that the crash box would suffer if subjected to an impact, that is to say the way in which it would collapse during the instants subsequent to the impact, which enables the crash box to be more accurately designed with respect to known inventions. Therefore beads of greater length can be designed than those present in the prior art inventions cited in the preamble: in fact, a bead may involve two or more walls of each portion of the deforming body or develop along a path that includes the entire width of the relative portion on which the bead itself is incorporated, i.e. along the fixing tabs and the walls of the half-shell. In this way, it is advantageously possible to guide the plastic deformation of the deforming body more precisely and more accurately adjust the amount of energy required to produce a certain degree of deformation of the deforming body as a result of an impact. BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will be described in the following, according to what is set out in the claims and with the aid of the accompanying tables of drawings, in which:

- figures 1 , 2 are two perspective views of a crash box of the present invention, according to a first embodiment;

- figures 3A-3H are perspective views of a test crash box at instants following an impact (compressive stress) acting along the longitudinal axis of the crash box;

- figures 4A-4H are perspective views of a crash box of a second embodiment of the invention at instants following an impact (compressive stress) acting along the longitudinal axis of the crash box;

= figure_5-illustrates-a-graph-showing-a-progression-over-time -of-the-force— with which the crash box of figures 3A-3H and the crash box of figures 4A- 4H reacts to an impact. DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to figures 1 , 2, 4A-4H, (1) denotes in its entirety a crash box, object of the present invention.

The crash box (1) comprises: a deforming body (2) configured such as to deform if subjected to an impact of a certain entity, the deforming body (2) comprising a first portion (3) and a second portion (4) which are opposite and fixed to one another such as to identify a tubular member (5) which has a first axis and comprises a first wall (6) and a second wall (7) adjacent to one another, which intersect to identify an edge (8).

Each portion (3, 4) comprises a half-shell (9) and two fixing tabs (10) arranged respectively at opposite ends of the half-shell (9), at least a portion (3, 4) comprising at least a bead (11 , 12) which develops along a perpendicular development with respect to the first axis, which bead (11 , 12) is conformed such as to guide the plastic deformation of the deforming body (2) and such as to regulate a quantity of energy required for producing a certain degree of deformation of the deforming body (2) following an impact.

The bead (11 , 12) develops continuously at least along a part of the first wall (6) and at least along a part of the second wall (7) of the tubular member (5), following at least the edge (8) identified between the first wall (6) and the second wall (7), the bead (11 , 12), when it follows the first wall (6), being orientated projecting with respect to the zone of the external surface of the first wall (6) which surrounds the bead (11 , 12), the bead (11 , 12), when following the second wall (7), being orientated retracted with respect to the zone of the external surface of the second wall (7) which surrounds the bead (11 , 12), the bead (11 , 12), at the edge (8), varying orientation thereof between projecting and retracted.

By "external surface" of the first wall (6) or the second wall (7) is meant the surface facing outwardly with respect to the tubular member (5); this external surface is opposite the internal surface of the first wall (6) or the second wall (7), which internal surface faces and defines the internal volume-together-with- the internal surfaces of the remaining walls (13) of the tubular member (5). A bead of the above-described type is illustrated by way of example in the crash box (1 ) of figuresl , 2 and denoted by reference numeral (12).

Each portion (3, 4) can be obtained by folding (or also by pressing) of a strip of sheet metal to obtain five walls (6, 7, 13), of which the two end walls (10), aligned to one another, i.e. lying on a same plane, conform the fixing tabs (10), while the remaining three internal walls (6, 7, 13) are angled to one another to form a geometrical figure, in the illustrated example a hexagon, when the two portions (3, 4) above are fixed to one another at the fixing tabs (10). The tubular member (5) that is obtained can for example conform a hexagonal cell formed by six internal walls (6, 7, 13), i.e. three internal walls (6, 7, 13) for each portion (3, 4), and by lateral projections each constituted by two fixing tabs (10) opposite to one another and joined together for example by spot welding.

The walls (6, 7, 13) are flat. Each portion (3, 4), in general, can conform a plurality of half-shells (9) (an embodiment not shown in the figures), so that when the two portions (3, 4) are fixed to one another an equal number of tubular members (5) are identified, flanked and each having, for example, a hexagonal cell profile, or square or octagonal, etc.

The bead (11 , 12) is, as mentioned in the preamble, a kind of channel, having a concavity of given depth, obtainable by compression of the sheet by deep drawing.

The crash box (1) is installed in the motor vehicle (not shown) in such a way that the longitudinal axis (first axis) of the tubular member (5) coincides with the direction of deformation in the event of a frontal impact.

The beads (11 , 12) may be several, located side by side and parallel to one another, on the walls (6, 7, 13) of the tubular member (5).

The crash box (1) shown in figures 1 , 2 comprises, for each portion (3, 4), two beads (11) situated side by side and parallel; each of the beads (11) extends along a path that includes the entire width of the relative portion (3, 4) on which the bead (11) itself is incorporated, i.e. along the fixing tabs (10) and the walls (6, 7, 13) of the half-shell (9). In this way it is advantageously possible to guide the plastic deformation of the deforming body (2) better, and more accurately regulate the amount of energy required to produce a certain degree of deformation of the deforming body (2) as a result of an impact.

When the first portion (3) is fixed to the second portion (4) such as to locate the tubular member (5), then a fixing tab (10) of the first portion (3) faces a corresponding fixing tab (10) of the second portion (4).

The beads (11) of the first portion (3) and the second portion (4) are preferably arranged such as to be facing one another, as shown in figures 1 , 2, 4A-4H; in particular, these beads (11) are oriented projectingly at the fixing tabs (10), such as to identify a channel which is closed above and below by the beads (11).

At least a portion (3, 4) of the body of deformation (2) may comprise at least one additional bead (14) which develops parallel to the first axis in order to increase the resistance to deformation of the deforming body (2) (figures 1 , 2). At least one fixing tab (10) can exhibit a free end that is folded, identifying a fold (15) to increase the resistance to deformation of the deforming body (2) (figures 1 , 2).

The fold (15) is preferably substantially perpendicular to the remaining part of the fixing tab (10).

Figures 3A-3H are perspective views of a "test" crash box in successive instants during an impact, and thus to a compressive stress, acting along the longitudinal axis (first axis) of the crash box; the crash box illustrated herein is not part of the present invention and is not known. The test crash box was used for the purposes of a comparative analysis with the crash box (1) according to the second embodiment, shown in figures 4A-4H, to highlight the greater efficiency of the latter crash box. For the purposes of this comparison, the magnitude of the impact and the direction in which the corresponding compressive stress acts (along the longitudinal axis of the crash box 1) are the same for both the test crash box of figures 3A-3H and and the crash box (1) of figures 4A-4H that is the object of the present invention.

Figures 3A, 4A illustrate the crash box at time instant: about 0.5 milliseconds. Figures 3B, 4B illustrate the crash box at time instant: about 1.5 milliseconds. Figures 3C, 4C illustrate the crash box at time instant: about 2 milliseconds. Figures 3D, 4D illustrate the crash box at time instant: about 2.5 milliseconds. Figures 3E, 4E illustrate the crash box at time instant: about 3 milliseconds. Figures 3F, 4F illustrate the crash box at time instant: about 3.5 milliseconds. Figures 3G, 4G illustrate the crash box at time instant: about 4 milliseconds. Figures 3H, 4H illustrate the crash box at the time instant: about 4.5 milliseconds.

Figure 5 shows, in a broken line, the time course of the force with which the crash box of figures 3A-3H reacts to a shock and reports, in a continuous line, the time course of the force with which the crash box (1) of figures 4A-4H reacts to a shock.

As can be seen in figure 5, the crash box (1) of the invention reacts to crushing with a less fluctuating and therefore more constant force, which maximizes the efficiency of the crash box (1) itself.

It is understood that the above has been described by way of non-limiting example, and that therefore possible constructiional variants are within the protective scope of the present technical solution, as claimed in the following.