Patent Description:
As is known, the drive shaft in internal combustion engines is subjected to torsional vibrations due to the periodic stress caused by the combustion in the cylinders. Such vibrations are particularly intense at the start and at low speeds, as well as in the presence of particular constructional solutions such as, for example, the use of double clutch gearboxes or start-stop systems.

The torsional vibrations result in rotational irregularities of the drive pulley of the accessory drive which are transmitted to the accessories by means of the drive belt, which is thus subjected to periodic tension variations.

With the object "to filter" the torsional oscillations transmitted from the crankshaft to the belt, a filtering pulley is generally used as drive pulley, said filtering pulley being provided with a hub integral with the drive shaft, a crown cooperating with the belt and one or more elastic elements through which the torque is transmitted from the hub to the crown. An example of such filtering pulley is illustrated in <CIT>.

Other known examples are shown in publications <CIT>, <CIT> or <CIT>.

One of the critical elements of the filtering pulley of the type described above is the relative rotation of the crown on the hub. In particular, the overrunning moments between crown and hub must be contained; furthermore, the need is felt to prevent the insertion of dust and debris between hub and crown causing noises and reducing the useful life of the filtering pulley.

The object of the present invention is to manufacture a filtering pulley which solves the aforementioned technical problem in a simple and cost-effective manner.

The aforementioned object is achieved by a filtering pulley according to what claimed in the appended claims.

In order to better understand the present invention, a preferred embodiment is described in the following, by way of non-limiting example and with reference to the accompanying drawings, wherein:.

In the accompanying figures, a filtering pulley <NUM> is represented comprising a hub <NUM> of axis A, adapted to be connected to a shaft (not represented), for example a crankshaft of an internal combustion engine, and an annular crown <NUM> externally coaxial to the hub <NUM> and supported in a rotationally free manner on the hub <NUM> by means of a supporting element <NUM>.

The crown <NUM> comprises an annular portion <NUM> provided with a profile <NUM> adapted to cooperate with a poly-V belt (not represented). The crown <NUM> further comprises a radial wall <NUM>, integral with the annular portion <NUM> and preferably of a single piece therewith, extending radially towards the hub <NUM>, and a substantially cylindrical internal wall <NUM> of axis A.

The crown <NUM> carries, integral thereto, a closing element <NUM> comprising an outer cylindrical wall <NUM> of axis A, a flat radial annular wall <NUM>. The closing element <NUM> is driven into the crown <NUM> so as to form an annular chamber <NUM> radially comprised between the wall <NUM> and the wall <NUM> and axially delimited by the wall <NUM> and the wall <NUM>.

The closing element <NUM> finally comprises two diametrically opposite projections <NUM> axially extending inside the chamber <NUM> starting from the wall <NUM> (see <FIG>). The projections <NUM> divide the chamber <NUM> into two portions 15a, 15b, preferably of equal dimensions.

On the wall <NUM> stop elements can be provided, such as further two projections (not illustrated) preferably arranged at <NUM>° with respect to the projections <NUM>, thus substantially in the middle of the respective aforementioned portions 15a, 15b of the chamber <NUM>. The projections <NUM> or the aforementioned stop elements are carried fixed by the respective walls or, alternatively, made of a single piece with the same.

The pulley <NUM> can further be provided with a dynamic damper <NUM> comprising a disc <NUM>, facing the closing element <NUM> and having a portion of hub <NUM> integral with the hub <NUM>, and a seismic ring <NUM> constrained to a peripheral flange <NUM> of the disc <NUM> by a ring <NUM> of elastomeric material.

As is illustrated, the pulley <NUM> further comprises at least one elastic group <NUM>, for example two elastic groups <NUM> arched and arranged circumferentially free in the respective portions 15a, 15b of the chamber <NUM> delimited by the projections <NUM>.

Each of the elastic groups <NUM> comprises at least one spring, in the described case a helical and arched spring <NUM> mounted between the aforementioned projections <NUM>.

The pulley <NUM> further comprises an actuator <NUM> carried integrally by the hub <NUM> and advantageously axially interposed between the hub <NUM> and the disc <NUM> of the dynamic damper <NUM>. The actuator <NUM> has two spokes <NUM> free to move circumferentially in the chamber <NUM> and adapted to interact with the elastic groups <NUM> by contact as described in the following.

Advantageously, the actuator <NUM> is carried by the hub <NUM> by means of a shape coupling <NUM>, for example by means of a pin <NUM> configured to be inserted in respective openings of the actuator <NUM> and of the hub <NUM>. Preferably, the shape coupling <NUM> allows the coupling also of the disc <NUM> of the dynamic damper <NUM> to the hub <NUM>, hence it comprises an opening adapted for the insertion of the pin <NUM>.

The actuator <NUM> can be placed in contact with the elastic groups <NUM>, possibly with a circumferential interference value so as to preload the elastic groups <NUM> inside the seat <NUM>. Alternatively, it can be placed with an angular interval with respect to the elastic groups <NUM>, i.e. an angular play before entering into contact with the same.

The pulley <NUM> can further comprise a dust protection system <NUM> configured to isolate the space <NUM> from the outside and extending between the wall <NUM> of the element <NUM> and the hub <NUM>.

According to the invention, the pulley <NUM> further comprises a dust protection lip <NUM> configured to prevent the contamination from the outside of the rotating support <NUM> between hub <NUM> and crown <NUM>. Furthermore, the dust protection lip <NUM> has the function of axial thrust bearing.

According to a further aspect of the invention, the rotating support <NUM> is a bush having an L-shaped section and provided with an annular cylindrical portion 4a and a radial wall 4b made of a single piece.

The cylindrical portion 4a is radially interposed in contact between the hub <NUM> and the wall <NUM> and the hub <NUM> is configured to support a radial load between crown <NUM> and hub <NUM>, whereas the radial wall 4b is placed axially in contact with the wall <NUM> and facing the actuator <NUM>, i.e. on the opposite side of the dust protection lip <NUM>, without contact with the same. The radial wall 4b is thus intended to contain possible axial loads acting on the crown <NUM>; in particular, it defines the light with respect to the actuator <NUM> and thus the maximum axial stroke of the same.

The dust protection lip <NUM> is axially interposed between a projection 2a of the hub <NUM> and the wall <NUM> connecting the walls <NUM> and <NUM>, advantageously in a radially external position with respect to the bush <NUM>. More specifically, the dust protection lip <NUM> is placed in contact between the wall <NUM> and the projection 2a.

In particular, the projection 2a defines an annular seat <NUM> adapted to house the dust protection lip <NUM>. The seat <NUM> is radially comprised between an axial projection <NUM> extending cantilevered from the projection 2a of the hub <NUM> and the outer surface of the remaining part of the hub <NUM>, axially it is open towards the wall <NUM>, whereas it is closed by a bottom wall of the projection 2a.

In particular, the bottom wall of the seat <NUM> has a variable height section, in particular an axial annular protrusion <NUM> configured to cooperate in contact with the dust protection lip <NUM> as described in the following.

The dust protection lip <NUM> comprises a central portion adapted to cooperate in contact with the bottom wall of the seat <NUM> and with the wall <NUM>. Consequently to what described above, the central portion 50a is configured to be inserted around the axial annular protrusion <NUM> so as to be axially fixed with respect to the hub <NUM>.

The dust protection lip <NUM> also comprises a lower radial lip 50c and an upper radial lip 50d respectively shaped for extending axially beyond the central portion 50a and radially above with respect to the same.

In particular, the lower radial lip 50c is configured to cooperate in contact with the wall <NUM>, whereas the upper radial lip 50d is configured to cooperate in contact with the axial projection <NUM>.

According to what described above, thanks to its geometry, the dust protection lip <NUM> is of labyrinthine type, i.e. defines a tortuous path between the external environment and the bush <NUM> effectively preventing the insertion of dust or debris towards it.

Advantageously, the dust protection lip <NUM> is made of polymeric material and of a single piece.

The operation of the pulley <NUM> is described in the following.

In a first operational step, called driving mode and constituting the normal operation of the pulley <NUM>, when the drive shaft pulls the accessories, the speed of the hub <NUM> tends to exceed the speed of the crown <NUM>. For this reason, the spokes <NUM> of the actuator <NUM> transmit the torque to the projections <NUM> with the interposition of the respective elastic groups <NUM>.

What described above occurs, symmetrically, in the overrunning condition, i.e. when the speed of the crown <NUM> tends to exceed the speed of the hub <NUM>.

Depending on the damping present between the hub <NUM> and the crown <NUM>, as known per se, a hysteresis can be present with respect to the two operations described above. In case of important angular variations which could damage the elastic groups <NUM>, the stop elements prevent excessive relative rotation between hub <NUM> and crown <NUM>.

The actuator <NUM> if in contact preloaded by or distanced from the elastic groups, allows an angular play between hub <NUM> and crown <NUM>.

During the movement between hub <NUM> and crown <NUM>, the dust protection lip <NUM> is pulled in its rotation around the axis A and slides with respect to the wall <NUM>. During such sliding, it has the function of preventing the dirt from reaching the bush <NUM> which is preserved from contaminations.

Furthermore, the bush <NUM>, during the relative rotational movement between hub <NUM> and crown <NUM> absorbs possible axial loads thanks to the L shape provided by the same.

The advantages of a pulley <NUM> according to the invention are thus evident.

Thanks to the dust protection lip <NUM> dirt elements are prevented from reaching the bush <NUM>, protecting the operation thereof, reducing the noises and increasing the life expectancy thereof.

The particular arrangement and shape of the dust protection lip <NUM> ensures an excellent sealing thanks to the anchoring on the axial annular protrusion <NUM> and to the labyrinthine path defined by the lips 50b, 50c.

Still, the presence of the bush <NUM> having an L-shaped section allows resisting against possible overrunning loads acting on the crown <NUM> with respect to the hub <NUM>.

Additionally, the bush <NUM> allows an easy mounting of the pulley <NUM>.

Furthermore, synergically, the configuration of the L-shaped bush <NUM> and the arrangement with respect thereto of the dust protection lip <NUM> further prevent dust or debris from being channelled between crown <NUM> and hub <NUM>, protecting the relative movement thereof and thus the useful life of the pulley <NUM>.

Finally, it is clear that modifications or variations can be made to the described pulley which do not depart from the scope of protection defined by the claims.

First of all, the pulley could be used not exclusively on the crankshaft of an internal combustion engine but for one of the accessories of the same.

With reference to the elastic group <NUM>, they could be manufactured without anyway modifying their function. For example, they could comprise springs of different nature or several springs, in series or in parallel. Still, the elastic groups could be four and likewise the spokes of the actuator.

The dynamic damper <NUM> could be absent and the actuator could be carried differently by the hub <NUM>.

Claim 1:
Filtering pulley (<NUM>) comprising a hub (<NUM>) adapted to be fixed to a shaft rotating around an axis (A), a crown (<NUM>) mounted coaxially and rotationally free on said hub (<NUM>), at least one elastic group (<NUM>) arranged circumferentially with respect to said hub (<NUM>) and said crown (<NUM>) and interposed, each, between a pair of first elements (<NUM>) integral with said hub (<NUM>) and between a pair of second elements (<NUM>) integral with said crown (<NUM>), said pulley (<NUM>) comprising a dust protection lip (<NUM>) carried integrally by said hub (<NUM>) and configured to slide, in tight manner, with respect to an element (<NUM>, <NUM>) integral with said crown (<NUM>), said dust protection lip (<NUM>) being a labyrinthine sealing lip, wherein said dust protection lip (<NUM>) is housed in a seat (<NUM>) realized on said hub (<NUM>) and is configured to extend in an axial direction to cooperate in contact with said element (<NUM>), characterized in that said seat (<NUM>) is axially defined, on one side, by a variable height surface, said dust protection lip (<NUM>) comprising a main body (50a) configured to cooperate in contact with said variable height surface to radially fix said dust protection lip (<NUM>) to said hub (<NUM>).