Patent Description:
As is well known, the drive shaft in an internal combustion engine is subject to torsional vibrations due to periodic stresses caused by combustion in the cylinders.

These torsional vibrations translate into rotation irregularities when operating and, in addition, are transmitted to the other components of the engine via the transmission member, usually a belt.

The torsional vibrations may, thus, make some engine components to resonate, causing NVH issues in the vehicle where the engine is installed when operating.

In order to dampen these torsional vibrations, the use of dampers of torsional vibrations, of the viscous fluid type, or, more simply, "torsional viscous dampers", is known.

A typical torsional viscous damper comprises:.

Specifically, the inertial mass is normally defined by a disc formed from a material of suitable mass and stiffness, usually a metal material, and housed inside the above-mentioned chamber in a bath of viscous damping fluid, normally based on silicone. Such a disc conveniently has an annular shape around the hub.

The lid is defined by a thin disc, with an annular shape around the hub, which is welded to the casing, to close the chamber, at two points: at the radially inner circular edge and at the radially outer circular edge.

Therefore, the two weldings extend axially, i.e., along a direction parallel to a longitudinal axis of the hub (i.e. of the damper).

In other words, the lid is firmly coupled and fixed to the casing in order to close the above-mentioned chamber using two circular and axial weldings.

More precisely, the casing delimits the chamber on three sides, while the lid closes and delimits the chamber on the remaining side.

In use, the damper is "planted" on the engine shaft and receives the torsional vibrations from this.

The kinetic energy produced by these torsional vibrations causes the inertial mass, which is contained in the chamber defined by the casing closed by the lid, to resonate. This causes the movement of the inertial mass inside the chamber.

The kinetic energy is, thus, transformed into heat via friction and, therefore, dissipated.

The Applicant has observed that the torsional viscous dampers of the type described above require additional improvements.

In addition, the Applicant has observed that, particularly for very high performance vehicle engines, it is desirable that the maximum damping constant is reached while reducing, as much as possible, the weight and cost per unit, without compromising the high speed and axial acceleration induced by the engine's crank shaft.

Document <CIT>, which discloses a torsional damper with a single welding, is considered as the closest prior art.

The purpose of this invention is to produce a torsional viscous damper that is highly reliable and inexpensive, and makes it possible to avoid at least some of the drawbacks specified above and connected to known torsional viscous dampers.

According to the invention, this purpose is achieved with a torsional viscous damper as claimed in the attached independent claims.

To better understand this invention, a preferred, but non-limiting, embodiment is described below, merely by way of example, and with the aid of the attached figures in which:.

With reference to the attached figures, reference number <NUM> denotes, as a whole, a damper of torsional vibrations, of the viscous fluid type, simply identified as a "torsional viscous damper" below.

The damper <NUM> comprises a hub <NUM> and is designed to be mounted on an engine shaft <NUM> (not illustrated), for example a crank shaft, to dampen the torsional vibrations transmitted by the engine to this shaft (in a known way not described in detail).

In particular, the damper <NUM> has a central rotation axis A, and the hub <NUM> is coaxial to the axis A and is designed to be axially engaged by the shaft <NUM>.

The damper <NUM> comprises a casing <NUM> and a lid <NUM> coupled to each other to delimit a closed chamber <NUM>, which is annular in relation (i.e. around) the axis A and containing a viscous damping fluid (of the known type not described in detail, for example a highly viscous, silicone-based fluid).

The damper <NUM> also comprises an inertial mass <NUM> housed in the chamber <NUM> so as to be immersed in the viscous fluid.

Specifically, the inertial mass <NUM> is normally defined by a disc formed from a material of suitable mass and stiffness, usually a metal material, and housed inside the above-mentioned chamber <NUM> in a bath of viscous damping fluid.

Preferably, but not necessarily, the inertial mass <NUM> is made of aluminium.

Alternatively, the inertial mass <NUM> is made of another metal material, for example steel, a steel alloy, or another metal alloy suitable for the purpose.

The disc defining the inertial mass <NUM> is, conveniently, annular around the hub <NUM>.

Conveniently, the inertial mass <NUM> can rotate around the axis A independently of the casing <NUM> and the lid <NUM>, i.e. it is not fixed firmly to the casing <NUM> and to the lid <NUM>, but is coupled to these using special sliding interfaces, e.g. bearings (not illustrated).

The viscous fluid surrounds the annular inertial mass <NUM>.

According to the invention, the damper <NUM> comprises a pair of half-shells <NUM>, <NUM>, of which a first half-shell <NUM> defines the casing and a second half-shell <NUM> defines the lid.

As can be seen in <FIG>, each half-shell <NUM>, <NUM> defines part of the chamber <NUM> and part of the hub <NUM>, and the half-shells <NUM>, <NUM> are axially coupled to each other to define, together, the chamber <NUM> and the hub <NUM>.

Specifically, each half-shell <NUM>, <NUM> comprises an annular recess that defines part of the chamber <NUM>.

More specifically, each half-shell <NUM>, <NUM> basically defines, in this way, one half of the chamber <NUM>. The chamber <NUM> is closed by mutual coupling of the half-shells <NUM>, <NUM>.

Again according to the invention, the half-shells <NUM>, <NUM> are fixed to each other by means of a single welding <NUM>, which extends angularly about the axis A.

In particular, the welding <NUM> is annular (or circular) around the axis A, i.e. it extends angularly and completely around the axis A.

Alternatively, the welding <NUM> may have a limited angular extension around the axis A, so as to define an individual welded section, or several welded sections, angularly distributed around the axis A, preferably equally spaced apart.

In the example illustrated, each half-shell <NUM>, <NUM> has an annular shape around the axis A to define the hub <NUM>.

Each half-shell <NUM>, <NUM> has a radially annular inner edge <NUM> facing the axis A and a radially annular outer edge <NUM> opposite the inner edge <NUM>, i.e. radially facing outside.

In particular, the inner edges <NUM> of the half-shells <NUM>, <NUM> coupled to one another define a wedged radial end <NUM> of the damper <NUM> configured to be fixed to the shaft <NUM> by engaging with the hub <NUM>.

In practice, the inner edges <NUM> radially delimit the hub <NUM>.

Similarly, the outer edges <NUM> of the half-shells <NUM>, <NUM> coupled to one another define a free radial end <NUM> of the damper <NUM>, which is opposite the wedged end <NUM>.

Advantageously, the above-mentioned single welding <NUM> is arranged at the free radial end <NUM>.

In light of what was described above, the damper <NUM> is formed from two half-shells <NUM>, <NUM> only welded together at a single point (i.e. at the free end <NUM>), in contrast to known torsional viscous dampers, which comprise a casing defined by a shaped rim wherein a chamber for the inertial mass is formed, and a lid defined by a metal ring and positioned to close the chamber made in the casing, wherein the lid is welded to the casing at two points, as described in the introductory part of this description.

Thanks to the configuration of the damper <NUM> according to this invention, a particularly weak point of the damper <NUM>, which is highly prone to breaking, i.e. the most radially inner welding, is eliminated. In fact, it is possible to avoid a highly defective point in the damper <NUM>, since the mechanical features of the material of the two half-shells <NUM>, <NUM> are not locally compromised at the most stressed points, which are usually near the hub <NUM> or, in any case, in the radially inner area of the damper <NUM>. In contrast, the material of the damper <NUM>, thanks to the presence of the two half-shells <NUM>, <NUM> in place of the known casing and lid and thanks to the presence of a single welding <NUM> arranged at the free end <NUM> (and thus radially outer), keeps the original mechanical features at the most stressed points.

Advantageously, the welding <NUM> extends between the half-shells <NUM>, <NUM> in the radial direction.

Specifically, each half-shell <NUM>, <NUM> comprises an axial annular coupling surface 4a, 5a at the corresponding outer edge <NUM>, i.e. near the outer edge <NUM> and at the free end <NUM> defined by the coupling of the half-shells <NUM>, <NUM>.

The coupling surfaces 4a, 5a of the coupled half-shells <NUM>, <NUM> are arranged facing one and in contact, as can be seen in enlarged view in <FIG>.

According to one aspect of the invention, the welding <NUM> is axially interposed between the coupling surfaces 4a, 5a and extends in a radial direction to the axis A, between the coupling surfaces 4a, 5a.

In other words, the welding <NUM> has a negligible extension in the axial direction compared to its extension in the radial direction, i.e. it basically extends only in the radial direction.

This configuration is particularly advantageous: the Applicant has, in fact, been able to verify that the resistance of the damper <NUM> to the axial stresses is significantly improved compared to known dampers, in which the lid is fixed to the casing via two axial weldings, i.e. having a negligible extension in the radial direction compared to its extension in the axial direction. These known weldings are, in fact, subject to strong axial stresses (even in the order of <NUM>) coming from the engine and, thus, are particularly prone to giving way, leading to a reduction in the service life of the damper <NUM>.

In addition, the inertial mass <NUM> is designed to push in the axial direction, adding an additional stress in this direction.

Thus, the radial welding <NUM> according to the invention mitigates this undesired effect and increases the service life of the damper <NUM>.

Advantageously, the damper <NUM> comprises a sealing ring <NUM> arranged axially between the half-shells <NUM>, <NUM> and radially interposed between the chamber <NUM> and the hub <NUM> and configured to prevent a leakage of the viscous fluid from the chamber <NUM> towards the hub <NUM>.

In practice, the sealing ring <NUM>, preferably made of elastomeric material, fills, without, in any case, introducing additional weaknesses and without compromising the features of the material, the sealing function that was performed by the radially inner second welding in the known dampers.

Preferably, the damper <NUM> comprises an additional sealing ring (not illustrated) arranged axially between the half-shells <NUM>, <NUM> and radially interposed between the chamber <NUM> and the free end <NUM>, i.e. between the chamber <NUM> and the welding <NUM>.

In this way, a leakage of the viscous fluid towards the welding <NUM> is also avoided, which improves the performance of the welding <NUM> as well as its service life.

As can be seen in <FIG>, each half-shell <NUM>, <NUM> includes a first radial portion <NUM> carrying the inner edge <NUM> and radially delimiting the hub <NUM>, and a second radial portion <NUM> carrying the outer edge <NUM> and delimiting the chamber <NUM>.

Specifically, the first portions <NUM> coupled to one another define a radially inner portion <NUM> of the damper <NUM>, and the second portions <NUM> coupled to one another define a radially outer portion <NUM> of the damper <NUM>.

According to one aspect of the invention, the radially inner portion <NUM> has a greater axial thickness than the axial thickness of the radially outer portion <NUM>.

In particular, the radially inner portion <NUM> has an axial thickness greater than the axial thickness of the radially outer portion <NUM>, of a value ranging between <NUM> and <NUM> times, preferably between <NUM> and <NUM> times, even more preferably between <NUM> and <NUM> times.

The Applicant has observed how this configuration improves the structural resistance of the damper <NUM>, since the radially inner portion <NUM> represents, as mentioned, the most stressed point of the damper <NUM> itself. In addition, this configuration reduces the total diameter of the damper <NUM> and of the axial dimensions of the same, without compromising performance - actually improving it.

Conveniently, one of the half-shells <NUM>, <NUM> (in the example illustrated, the half-shell <NUM>) comprises, at the outer edge <NUM> (i.e. near the outer edge <NUM> and at the free end <NUM> defined by the coupling of the half-shells <NUM>, <NUM>), a first axial protuberance <NUM> extending towards the other of said half-shells <NUM>, <NUM> and engaging a corresponding axial seat <NUM> formed in the other of said half-shells (in the example illustrated, the half-shell <NUM>), so that the two half-shells <NUM>, <NUM> have a complementary shape when coupled, preferably via interference, at said free ends <NUM>.

Similarly, one of the half-shells <NUM>, <NUM> (in the example illustrated, the half-shell <NUM>) comprises, at the inner edge <NUM> (i.e. near the inner edge <NUM> and at the wedged end <NUM> defined by the coupling of the half-shells <NUM>, <NUM>), a second axial protuberance <NUM> extending towards the other of said half-shells <NUM>, <NUM> and engaging a corresponding axial seat <NUM> formed in the other of said half-shells (in the example illustrated, the half-shell <NUM>), so that the two half-shells <NUM>, <NUM> have a complementary shape when coupled, preferably via interference, at said wedged end <NUM>.

Each protuberance <NUM>, <NUM> is preferably defined by an annular flange projecting axially towards the other of the half-shells <NUM>, <NUM>.

As a result, the seats <NUM>, <NUM> are annular and extend, in the other of the half-shells <NUM>, <NUM>, in the axial direction.

Alternatively, the flanges <NUM>, <NUM> could be defined by multiple, corresponding axial protuberances angularly distributed around the axis A, so as to define corresponding interrupted rings. As a result, the seats <NUM>, <NUM> would also in this case be defined by recesses angularly distributed around the axis A.

As shown in <FIG>, each flange-seat coupling defines an axial shoulder for one or the other half-shell <NUM>, <NUM>.

This configuration provides a simple tool for ensuring the correct centring of the two half-shells <NUM>, <NUM> thus facilitating their mutual coupling.

The second flange <NUM> is, preferably, radially interposed between the sealing ring <NUM> and the hub <NUM>.

Therefore, the presence of the flanges <NUM>, <NUM> and of the seats <NUM>, <NUM>, i.e. the presence of the axial shoulders, provides an additional means of sealing the viscous fluid. In fact, each shoulder defines a kind of labyrinthine path that makes it more difficult for the viscous fluid to leak out.

It should be noted that, in <FIG>, the left half-shell <NUM> denotes the casing, while the right half-shell <NUM> denotes the lid. In any case, this configuration is totally arbitrary.

In fact, according to one aspect of the invention, the half-shells <NUM>, <NUM> have a basically symmetrical shape to each other in relation to a median radial plane (not illustrated) in relation to the axis A.

In practice, the damper <NUM> comprises two half-shells <NUM>, <NUM> that are basically equal (in particular, without said flanges <NUM>, <NUM> and seats <NUM>, <NUM>) and complementary with each other and in place of the normal casing and lid - mentioned above - of known dampers.

Thanks to this peculiar structural feature, the damper <NUM> is more balanced in terms of stresses in relation to known dampers, which have two pieces (casing and lid) with a totally different stiffness and shape, which results in an unbalanced structure prone to strong vibrations at certain speeds.

On the contrary, the stiffness of each half-shell <NUM>, <NUM> is basically identical, resulting in the above-mentioned structural balancing of the damper <NUM> produced according to the invention and, thus, in an improvement in its performance.

In addition, the above-mentioned peculiar shape of the half-shells <NUM>, <NUM> results in an improvement of the production process for the damper <NUM>: a single forging mould (or moulding) to produce both half-shells <NUM>, <NUM> will, in fact, be enough, before then producing the finishings (for example, the flanges <NUM>, <NUM> and the seats <NUM>, <NUM>) via mechanical processing. On the contrary, for known dampers, two different types of mould are necessary for the casing and lid.

This, therefore, makes it possible to reduce production costs and times.

The half-shells <NUM>, <NUM> are preferably made of metal, in particular aluminium.

Conveniently, the damper <NUM> also comprises clamping means (not illustrated) for axially clamping the half-shells <NUM>, <NUM> together.

In one embodiment, the clamping means comprise screws extending through the radially inner portion <NUM> in the axial direction.

The clamping means assist in supporting the torsional stresses, which, thus, offload onto the clamping means, avoiding stressing the welding <NUM> too much.

The advantages afforded by the damper <NUM> produced according to this invention are apparent from an examination of the characteristics thereof.

In particular, thanks to the peculiar shape of the damper <NUM>, according to this invention:.

Claim 1:
A torsional viscous damper (<NUM>) for damping torsional vibrations transmitted to a shaft (<NUM>) of an engine, the damper (<NUM>) having a central rotation axis (A) and comprising:
- a casing (<NUM>) and a lid (<NUM>) coupled together for delimiting a closed chamber (<NUM>), annular with respect to the central axis (A) and containing a viscous damping fluid; and
- an inertial mass (<NUM>) housed in the chamber (<NUM>) so as to be immersed in the viscous fluid;
wherein:
- the damper (<NUM>) comprises a pair of half-shells (<NUM>, <NUM>), a first half-shell (<NUM>) defining the casing and a second half-shell (<NUM>) defining the lid, each half-shell (<NUM> , <NUM>) defining part of said chamber (<NUM>) and part of an axial hub (<NUM>) configured to be engaged by said shaft (<NUM>),
- the half-shells (<NUM>, <NUM>) are axially coupled to one another for defining together said chamber (<NUM>) and said hub (<NUM>),
- the half-shells (<NUM>, <NUM>) are fixed to each other by means of a single welding (<NUM>) which extends angularly about the central axis (A);
characterised in that
each half-shell (<NUM>, <NUM>) has an annular shape around the central axis (A) for defining said hub (<NUM>), each half-shell (<NUM>, <NUM>) having an inner edge (<NUM>) radially facing the central axis (A) and an outer edge (<NUM>) radially opposite to the inner edge (<NUM>);
- the inner edges (<NUM>) of the half-shells (<NUM>, <NUM>) coupled to one another define a wedged radial end (<NUM>) of the damper (<NUM>) configured to be fixed to said shaft (<NUM>) ;
- the outer edges (<NUM>) of the half-shells (<NUM>, <NUM>) coupled to one another define a free radial end (<NUM>) of the damper (<NUM>);
and wherein said single welding (<NUM>) is arranged at the free radial end (<NUM>).