FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a mold for manufacturing toothed sprockets for locking winding rollers of safety belts.

The invention also pertains to a process for manufacturing toothed sprockets.

It is known that rewinding rollers for safety belts, of the type commonly used on motor-vehicles for example, usually comprise a toothed sprocket essentially including a disc-shaped element carrying a circumferential toothing, which is coaxially associated with a winding roller of the safety belt. Rotation of the sprocket is locked when, upon intervention of an accelerometer operating device, a toothed fork is brought to a working condition of mutual meshing with the sprocket toothing.

Since the toothed sprocket is a component on which persons' safety relies in case of accident, strict parameters must be observed in terms of geometric and dimensional tolerance, to supply suitable reliability guarantees in time.

These requirements are presently met by making the toothed sprockets of an aluminum alloy molded by pressure die-casting.

In detail, die-casting is carried out through injection of a molten aluminum alloy into a mold in which a plurality of molding cavities or so-called â€œmold impressionsâ€ are defined, each corresponding to a toothed sprocket to be obtained, mutually connected by runners opening into at least one aperture or gate for admission of molten metal.

These runners each communicate with the molding cavity at a peripheral circumferential region of the cavity itself adapted to define the toothing of the respective sprocket.

In this way, the molten metal is introduced into each cavity through a respective runner along an injection path substantially perpendicular to the longitudinal extension axis of the toothed sprocket. Once introduced into the molding cavity, the molten metal flows along a predetermined path filling the whole cavity so as to conform in shape to the cavity itself.

However, many difficulties have been found in obtaining toothed sprockets in which the presence of tailpieces projecting at right angles from the disc-shaped body is required, for example for supporting and/or mechanically cooperating with other components of the rewinding device of the safety belt.

In fact, these tailpieces having an extension parallel to the longitudinal axis of the sprocket, are not formed in a correct manner because the molten metal does not successfully fill the cavities formed in the molds in order to obtain said tailpieces.

In this regard the Applicant has noticed that during the die-casting step the molten metal tends to follow the main cavity of the mold according to the path imposed by the runners, and it does not always succeed in efficiently filling the secondary cavities extending transversely of said path, before the metal solidifies.

Also when said secondary cavities are filled with molten metal, the latter does not flow thereinto with the required pressure, thereby generating tailpieces internally having air bubbles weakening their structure.

OBJECT OF THE INVENTION

In the light of the above, it is an object of the present invention to provide a process and a mold for manufacturing toothed sprockets for locking winding rollers of safety belts capable of solving the above mentioned drawback.

In particular, it is an object of the present invention to propose a process and a mold for manufacturing toothed sprockets for locking winding rollers of safety belts, capable of ensuring a better filling of the mold, so as to enable projecting portions or tailpieces having optimal mechanical features to be obtained.

SUMMARY OF THE INVENTION

The technical task mentioned and the objects specified are substantially achieved by a process and a mold for manufacturing toothed sprockets for locking winding rollers of safety belts according to the features recited in the appended claims.

More particularly, the invention proposes a process for manufacturing a toothed sprocket for locking winding rollers of safety belts, comprising the steps of: providing a mold having a main cavity defining at least one toothed disc-shaped body and at least one secondary cavity, brought into fluid communication with the main cavity so as to define a tailpiece jutting out of said toothed disc-shaped body; die-casting a molten metal alloy in said main cavity along a filling path of same;

wherein during the die-casting step at least part of the molten metal alloy meets at least one deflecting element provided along the filling path for deviating the alloy towards said secondary cavity.

According to a further aspect, the invention proposes a mold for manufacturing toothed sprockets for locking winding rollers of safety belts, comprising: a main cavity adapted to be filled with a molten metal alloy so as to define at least one toothed disc-shaped element having a toothing on a peripheral surface thereof; and at least one secondary cavity brought into fluid communication with said main cavity, so as to define a tailpiece jutting out of the disc-shaped body; characterized in that it comprises at least one deflecting element extending within the main cavity for deviating the metal alloy towards said secondary cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

Description of a preferred but not exclusive embodiment of a process and a mold for manufacturing toothed sprockets for locking winding rollers of safety belts is now given hereinafter by way of non-limiting example and illustrated in the accompanying drawings, in which:

FIG. 1 is a fragmentary section view of a mold for manufacturing toothed sprockets for locking winding rollers of safety belts in accordance with the present invention;

FIG. 2 is a perspective view of a toothed sprocket obtained with the method of the present invention; and

FIG. 3 is a further perspective view of the toothed sprocket seen in FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

With reference to the drawings, a mold for manufacturing toothed sprockets in accordance with the present invention has been generally identified by reference numeral 1. The toothed sprockets 100 obtained following the method of the present invention are intended for locking winding rollers of safety belts.

With reference to the drawings, a mold for manufacturing toothed sprockets in accordance with the present invention has been generally identified by reference numeral 1. The toothed sprockets 100 obtained following the method of the present invention are intended for locking winding rollers of safety belts.

In particular, sprocket 100 is locked when, upon intervention of an accelerometer operating device, a toothed fork (not shown) is brought to a working condition of mutual meshing with a tooth 101 of sprocket 100.

As shown in FIGS. 2 and 3, the toothing 101 of sprocket 100 is circumferentially distributed on the periphery of a disc-shaped body 102 which preferably extends radially away from a cylindrical central portion 103.

Said central portion 103 is rigidly connected to a rotating member of the winding device. In the embodiment shown, the cylindrical central portion 103 has a through central hole comprising a plurality of grooves 104 intended for coupling with respective mating toothing series provided on a hub or shaft carried by a winding roller of safety belts.

Sprocket 100 further comprises one or more tailpieces 105 (two tailpieces in the preferred embodiment) extending perpendicular to, or in any case transversely of a diametrical plane of the disc-shaped body 102 carrying toothing 101, as shown in FIG. 2.

Mold 1 is adapted to make a sprocket 100 of the above described type which comprises a first half 2 and a second half 3 having respective surfaces 2a, 3a that can be mutually faced, so as to define a main cavity 4.

The shape of the main cavity 4 of mold 1 matches the shape of at least the sprocket portion consisting of the radial toothing 101 and the disc-shaped body 102.

In the preferred embodiment, the shape of the main cavity 4 further matches the shape of the cylindrical portion 103 of the toothed sprocket 100.

In this way, through die-casting of a molten metal, preferably an aluminum alloy, into the main cavity 4, toothing 101, disc-shaped body 102 and cylindrical portion 103 of sprocket 100 can be defined.

In this regard, mold 1 comprises an injection runner 5 radially opening into the main cavity 4 at a gate 5a in a direction X substantially parallel to the diametrical extension plane of the main cavity 4, as shown in FIG. 1.

To make said tailpieces 105 jutting out of sprocket 100, mold 1 further comprises one secondary cavity 6 for each tailpiece 105.

In particular, each secondary cavity 6 is fully formed in the first 2 and second 3 halves and is brought into fluid communication with the main cavity 4.

The secondary cavity 6 has a longitudinal extension direction oriented transversely of a diametrical extension plane of the main cavity 4.

The metal alloy die-cast through the injection runner 5 passes through the gate 5a in the extension direction X of the injection runner, and spreads in the main cavity 4 following a filling path represented just as an indication by arrow P in FIG. 1.

Advantageously, to ensure correct and efficient filling of the secondary cavity 6 thereby giving the tailpieces 105 of sprocket 100 the necessary mechanical features, mold 6 comprises a deflecting element 7 extending in the main cavity 4 along the filling path P.

In more detail, the deflecting element 7 is disposed in front of gate 5a, along the extension direction X of the injection runner 5. Consequently, at least part of the metal alloy die-cast along the entry path P meets the deflecting element 7 and is therefore deviated in a direction transverse to the diametrical extension plane of the main cavity 4, i.e. towards the secondary cavity 6.

In the preferred embodiment shown in FIG. 1, the deflecting element 7 is formed in half 3 disposed opposite to half 2 in which the secondary cavity 2 is formed, in alignment relationship with the longitudinal extension direction of the secondary cavity, and has a substantially conical conformation with rounded vertex, so as to define an oblique surface 8 relative to the flow direction of the metal alloy from the injection runner 5, in such a manner that the deviating action of the filling path is optimized.

The deflecting element 7 projects from a surface 3a of half 3 of mold 1. Consequently, the presence of the deflecting element 7 creates a recess 106 shown in FIG. 3, in the disc-shaped body 102 of sprocket 100, at tailpiece 105. This recess 106 can be easily identified and denotes the presence of the deflecting element 7 in mold 1.

When the molten metal alloy has been die-cast into mold 1 and the main cavity 4 and secondary cavity 6 are filled, the molten metal solidifies by cooling. When solidification is over, the two halves 2, 3 are moved apart from each other and sprocket 100 is drawn out of the mold.

Possible sprues or flashes are then removed from sprocket 100 in the subsequent finishing steps.

The invention achieves the above specified purposes and in addition allows elimination of possible pockets due to solidification shrinkage that could be formed in the disc-shaped body 102 at the surface opposite to tailpiece 105. In fact, due to the presence of the deflecting element 7, there is more homogeneity of the material in terms of thickness at said tailpiece 105, and possible volume variations resulting from solidification can be compensated for by an increase in the sizes of recess 106.