Improved filtering pulley

Abstract

Filtering pulley (1) for an accessory transmission of an internal combustion engine, comprising a hub (2), an annular crown (3) provided with a profile configured to cooperate with an endless transmission element (5), externally coaxial around an axis (A) to the hub (2) and supported in rotationally free motion on the hub, and a filtering unit (4) for transmitting the torque interposed between the hub (2) and the crown (3) and comprising a torsion spring (11), a carrier (12) and a torque limiting joint (20), the pulley (1) comprising a first and a second rolling support (6', 6'') respectively operationally interposed between said head element (7) and said hub (2).

Description

[0001] " IMPROVED FILTERING PULLEY"

[0002] Cross-Reference to Related Applications

[0003] This Patent Appl ication claims priority from Italian Patent Application No . 102024000010387 filed on May 8 , 2024 , the entire disclosure of which is incorporated herein by reference .

[0004] Technical Field

[0005] The present invention relates to a filtering pulley, in particular for a belt drive of an internal combustion engine for a motor vehicle .

[0006] The present invention is preferably, although not exclusively, applied to the pulley for actuating an alternator of an internal combustion engine . In the following, reference will be made to such application by way of example , it being clear , however, that the pulley of the invention can be utilized as driving pulley connected to the drive shaft or as driven pulley for dragging any other accessory of the engine , for example a reversible electric machine having the function of generator and motor .

[0007] State of the Prior Art

[0008] The use of a filtering pulley in motor vehicles is known for dragging the alternator by means of the accessory transmission belt .

[0009] Such pulley comprises a hub adapted to be connected to the rotor of the alternator, an annular crown provided with a profile adapted to cooperate with the belt and a filtering unit interposed between the hub and the crown of the pulley so as to avoid subj ecting the belt to dynamic overloads in the presence of torsional vibrations of the drive shaft or of rapid speed variations of the engine .

[0010] The filtering unit generally comprises a spring, for example a helical or spiral spring, or a plurality of springs or other elastic elements arranged circumferentially between the hub and the crown .

[0011] Since the alternator has a relatively high equivalent inertia and tends to drag the pulley in the presence of instantaneous reductions in the speed of the drive shaft , it is known to incorporate in the filtering unit a freewheel adapted to unidirectionally transmit the motion of the crown to the hub (normal operating condition) but to decouple the hub from the crown in case of torque reversal .

[0012] The introduction of start-stop systems in which a reversible electric machine is utili zed having the function of starting motor or alternator depending on the operating conditions makes it impossible to utili ze a filtering pulley with freewheel because this would decouple the electric machine , when it is driving, from the belt drive .

[0013] In order to solve this problem, solutions have been proposed in which the filtering unit comprises a spring constrained at its ends to respective elements coupled to the hub and to the pulley, respectively, with a relative freedom of rotation having predetermined excursion .

[0014] An example of known solution to such problem is illustrated in WO 2015 / 198277 Al . However, such solution does not yet result to be suf ficiently optimi zed in order to guarantee the desired technical performance . Moreover, such solution results to be radially and axially bulky .

[0015] In particular, the inertia of the crown is such that , summed to that of the rotor of the electric machine , it invalidates the filtering functionalities of the pulley .

[0016] The need is thus felt to provide a filtering pulley which can be utili zed both in a start-stop system and in a conventional transmission system, which enables solving the problems of the known filtering pulleys set forth above .

[0017] Another obj ect of the present invention is to manufacture a filtering pulley, which is compact and cost- ef fective to produce .

[0018] Summary of the Invention

[0019] The aforementioned obj ect is achieved by a pul ley as claimed in the appended independent claims .

[0020] Further preferred embodiments of the invention are embodied according to the claims which are dependent on or connected to the aforementioned independent claims . Brief Description of the Drawings

[0021] 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 appended drawings wherein :

[0022] • Figure 1 is a longitudinal section view of a pulley according to the invention; and

[0023] • Figure 2 is an exploded perspective view of the pulley of Figure 1 .

[0024] Detailed Description of the Invention

[0025] With reference to Figures 1 and 2 , a pulley 1 is illustrated essentially comprising a tubular hub 2 , a tubular crown 3 externally coaxial to the hub 2 and supported in a rotationally free manner on the latter and a filtering unit 4 for transmitting the torque operationally interposed between the hub 2 and the crown 3 . The hub 2 and the crown 3 are coaxial around a longitudinal axis A.

[0026] The hub 2 is adapted to be rigidly fixed to a shaft , not illustrated, of an accessory member of an internal combustion engine , for example an alternator or a reversible electric machine having the function of alternator and starting motor in a start-stop system .

[0027] In particular, the hub 2 comprises a tubular cylindrical portion 2a internally defining a coupling portion 2c to the aforementioned shaft between a first end 2a' and a second end 2a' ' of the cylindrical portion 2a . The hub 2 also comprises a flanged portion 2b radially extending from one 2a' ' of the end portions towards the crown 3 and provided with a radial portion 2b' extending perpendicular to the axis A and a longitudinal portion 2b' ' extending cantilevered from the radial portion 2b' parallel to the axis A towards the other end 2a' of the hub 2 .

[0028] The crown 3 essentially comprises an annular portion 3a having an essentially cylindrical shape .

[0029] Speci fically, the crown 3 defines a multi-groove profile 3b adapted to cooperate with an endless transmission element 5 , such as a poly-V belt ( a section o f which is schematically indicated in Figure 1 ) . The profile 3b is made on an external surface 3 ' of the annular portion 3a opposite an internal surface 3 ' ’ cooperating with the filtering unit 4 .

[0030] Speci fically, the annular portion 3a has a lower moment of inertia than that of the hub 2 and of the elements integral with the hub 2 , which are described in the following .

[0031] Speci fically, the radial extens ion of the annular portion 3a is of a smaller order of magnitude with respect to the axial extension, i . e . along the longitudinal axis A, with the exception of the zone defining the profile 3b, for obvious constructive reasons relative to the profile supporting the poly-V belt . The crown 3 is supported on the hub 2 by means of rolling supporting means. In particular, the pulley 1 comprises a first rolling support 6' and a second rolling support 6' ' . Specifically, the rolling supports 6' , 6' ' both comprise ball bearings and more specifically are identical to each other.

[0032] More specifically, the first rolling support 6' is radially interposed between the crown 3 and the first end 2a' of the hub 2. In particular, it is supported on the hub 2 by means of a head element 7 driven in the first end 2a' , in order to mount the pulley 1.

[0033] On the other hand, the second rolling support 6' ' is radially interposed between the crown 3 and the second end 2a' ' of the hub 2, i.e. between the longitudinal portion 2b' ' and the internal surface 3' ’ of the crown 3.

[0034] In particular, the seal element 7 defines an annular portion 7' and a radial flange 7 ’ ’ axially adjacent to the first rolling support 6' .

[0035] The radial portion 2b' of the flanged portion 2b is similarly axially adjacent to the second rolling support 6' ’ .

[0036] The aforementioned portions axially adjacent to the rolling supports 6' , 6' ' are adapted to support possible axial loads acting between hub 2 and crown 3 so as to compensate each other along the longitudinal axis A. The first and the second rolling supports 6 ' , 6 ' ’ are placed on axially opposite sides of the pulley 1 . In particular, the second rolling support faces a lid 10 separating the space 9 from the external environment .

[0037] A space 9 is thus defined between crown 3 and hub 2 radially delimited between the internal surface 3 ' ’ of the crown 3 and by the external surface of the cylindrical portion 2a of the hub 2 and axially delimited between the rollingly / slidingly supporting means described above .

[0038] The pulley 1 can also comprise a lid 10 configured to axially delimit one of the ends of the pulley 1 , and advantageously configured to be housed inside the crown 3 , i . e . radially cooperating in contact with the latter .

[0039] The filtering unit 4 is housed in the space 9 and essentially comprises a torsion spring 11 , a spring holding element 12 , in the following called carrier, cooperating with an end of the spring 11 and with a damping ring 13 axially interposed between the carrier and the head element 7 .

[0040] The carrier 12 cooperates in contact by sliding, i . e . axially slides in contact , with the head element 7 . With reference to Figure 1 , the carrier 12 has an annular shape and defines an annular wall 12 ' coaxial to the axis A and a radial wall 12 ' ’ radially extending towards the axis A starting from an axial edge of the annular portion 12 ' . Such radial wall 12 ' ' is configured to slidingly cooperate with the head 7 on a first side , whereas on a second side opposite the previous one it defines an internal radial protrusion 14 configured to house a spring blocking element 15 . In particular, the spring blocking element 15 comprises an axial proj ection axially extending along the axis A from the internal radial protrusion 14 and configured to cooperate in contact with an end of the spring 11 .

[0041] As shown in Figure 2 , the head 7 of the hub 2 defines a pair of proj ections 16 axially extending along the axis A starting from the annular portion 7 ' towards the carrier 12 . Clearly, such proj ections can have any angular distance in circumferential direction with respect to each other . In particular, such proj ections are arranged at 180 ° with respect to each other .

[0042] The carrier 12 defines a pair of radial proj ections 17 configured to cooperate with the axial proj ections 16 of the head 7 . In particular, such radial proj ections 17 radially extend starting from the radial wall 12 ' ’ of the carrier 12 .

[0043] Advantageously, the carrier 12 also defines an axial proj ection 18 extending from the annular wall 12 ' . Speci fically, in the illustrated embodiment , such axial proj ection 18 extends circumferentially around the axis A so as to delimit a seat 19 .

[0044] The spring 11 is preferably a helical spring having a rectangular section wire and comprising a plurality of coils winding around the axis A between the carrier 12 and the flanged portion 2b of the hub 2 . As mentioned above , one end portion of the spring 11 cooperates in contact with the spring holder 15 whereas the opposite end cooperates in contact with a respective spring holder , not visible , made in the flanged portion 2b . Consequently, the flanged portion 2b is configured to radially wind, in part , the spring 11 .

[0045] The damper 13 es sentially comprises an annular element made of a polymeric material having an "L"-shaped section and thus provided with a longitudinal portion 13 ' radially interposed between the carrier 12 and the internal surface 3 ' ’ of the crown 3 and an axial portion 13 ' ’ axially interposed between the carrier 12 and the head 7 . The annular element is coupled, by friction or by shape coupling, to the carrier 12 and therefore is integral with it around the axis A.

[0046] The pulley 1 further comprises a torque limiting j oint 20 essentially comprising a strip spring 21 housed in the space 9 and configured to simultaneously carry out the function of freewheel in both relative rotation directions between crown 3 and hub 2 . Advantageously such freewheel ef fect is provided at di f ferent levels of torque which can be transmitted between hub 2 and crown 3 in one direction with respect to another one . In particular, the torque limiting joint 20 is dimensioned to cooperate in contact with the hub 2 and the carrier 12 for decoupling the crown 3. In particular, the limiting joint 21 is housed in the space 9 in contact with the internal surface 3' ’ of the crown 3.

[0047] More specifically, the strip spring 21 has a substantially open-ring shape with two ends 21' , 21' ’ delimiting a space 22 between them. The strip spring 21 is mounted with radial interference inside the internal radial surface 3' ’ of the crown 3, in particular in a machine-worked zone 23. In particular, the zone 23 is machine worked for defining a grooved / waved surface, of the "ribbed" type having dimensions adapted to enable a predefined friction between strip spring 21 and crown 3.

[0048] The strip spring 21 has an axial dimension substantially constant along its entire circumferential extension and preferably has a rectangular section.

[0049] However, one of the two end portions 21' , 21' ’ defines at least one projection 24, 25. In particular, a first projection 24 extends in a circumferential direction starting from the end portion 21' towards the opposite end portion 21' ’ inside the space 22 and a second projection 25 axially extends along the axis A from an axial edge of the strip spring 21 towards the carrier 12.

[0050] The second projection 25 is axially dimensioned to cooperate in contact in circumferential direction within the circumferential edges of the seat 19 defined by the proj ection 18 ( or alternatively with smaller circumferential extension, directly with it ) .

[0051] Alternatively to or in combination with the presence of the proj ection 25 , the torque limiting j oint 20 also comprises an actuator element housed in the space 22 and configured to cooperate in contact within the seat 19 defined by the proj ection 18 of the carrier 12 so as to increase or decrease the opening of the strip spring 21 when the actuator element acts with them .

[0052] Advantageously, the actuator element comprises a metal lever 28 housed in the space 22 and interposed circumferentially between the end portions 21 ' , 21 ' ’ of the strip spring 21 and configured to cooperate in contact with the proj ection 24 and the end portion 21 ' ' , circumferentially, and extending in axial direction so as to cooperate circumferentially in contact within the seat 19 defined by the proj ection 18 of the carrier 12 . In such embodiment , the proj ection 25 thus does not cooperate in contact with the proj ection 17 and may not be present on the strip spring 21 .

[0053] According to an alternative embodiment , not illustrated, the strip spring 21 can comprise a further axial proj ection on the opposite side of the proj ection 25 and configured to cooperate with a respective proj ection carried by the hub 2 .

[0054] The operation of the embodiment of the pulley 1 according to the above-described invention is the following, referring to the embodiment comprising the lever 28 .

[0055] In normal conditions , namely when the crown 3 dragged by the belt 5 leads the hub 2 and thus tends to overtake it ( drive mode ) , the strip spring 21 rotates integrally with the crown 3 and the hub 2 is resistant .

[0056] Imagining a starting condition in which the proj ections 17 and 16 are in contact with each other, the torsion spring 11 tends to compress itsel f dragged by the hub 2 transmitting torque to the crown 3 in a filtered manner . During such compression the carrier 12 starts rotating, in turn, coming into contact with the lever 28 with a circumferential edge of the seat 19 , spreading the strip spring 21 , increasing the adherence thereof and enabling the supply of torque to the hub 2 by means of the torsion spring 11 . Once a maximum transmittable torque is reached, equal to that of adherence between the strip spring 21 and the internal surface 3 ' ’ of the crown 3 , the strip spring 21 s lips with respect to such internal surface thereby decoupling the crown 3 and the hub 2 .

[0057] In the case where , instead, the hub 2 tends to overtake the crown 3 ( overrunning ) , the torsion spring 21 rotates integrally with the crown 3 and i s resistant with respect to the hub 2 .

[0058] Imagining to be in the decoupling condition described in the foregoing, the crown 3 tends to rotate in opposite direction with respect to the hub 2 bringing the lever 28 to close the strip spring 21 . In such condition, the strip spring 21 tends to release itsel f decoupling from the surface of the crown 3 .

[0059] I f the lever 28 is not present , the operation is similar and in the driving torque condition the coupling occurs directly between the proj ection 25 within the seat 19 of the pro j ection 18 .

[0060] I f the further proj ection on the opposite side of the proj ection 25 is present , it aids limiting the expansion of the strip spring 21 , guaranteeing the sliding between pulley 3 and strip spring 21 .

[0061] Based on the foregoing, the advantages of a pulley 1 according to the invention are evident .

[0062] With respect to the known solutions which provide for the use of a freewheel , the present invention equipped with torque limiting j oint 20 enables obtaining a bidirectional coupling between hub and pulley, at least within a predetermined range of torques , making the use of the pulley in start-stop systems possible .

[0063] In particular, the use of two rolling supports allows withstanding greater transmittable torques and consequently greater radial loads acting on the crown, enabling the application of the component in contexts of vehicles with high requirements of loads and useful li fe .

[0064] Still , the presence of axial shoulders supporting such rolling supports enables recovering incident axial loads between hub and crown, reducing vibrations , noise and thus increasing the useful li fe of the same .

[0065] Furthermore , the use of two rolling supports of same type reduces the costs of the pulley .

[0066] Additionally, the moment of inertia of the crown results to be particularly reduced due to the substantially cylindrical shape of the same .

[0067] Speci fically, it results that the radial extension of the crown is of a smaller order of magnitude than the axial extension; the moment of inertia o f the same is smaller than that of the hub and of the elements rotating with it , with the aim to have a negligible moment of inertia of the crown with respect to that of the hub and of the parts rotating with it for enabl ing a more ef fective filtering of the torque oscillations .

[0068] Finally, it is clear that modi fications and variations can be made to the pulley 1 according to the present invention which anyway do not depart from the scope of protection defined by the claims . In particular, the spring 21 could be coupled to the hub 2 instead of the crown 3 .

[0069] The lever 28 , as mentioned, can be omitted in the case where the adherence between the spring 21 and the surface 3 ' ’ of the crown 3 ( or of the hub 2 ) in the drive mode is suf ficient for transmitting the required torques .

[0070] Similarly, further proj ections to the strip spring or to the hub can be provided .

[0071] The pulley can be used as driving pulley on the drive shaft instead of on the alternator and can also be utili zed on an alternator of conventional type or any other accessory .

Claims

CLAIMS1.- Filtering pulley (1) for an accessory transmission of an internal combustion engine, comprising a hub (2) , an annular crown (3) provided with a profile configured to cooperate with an endless transmission element (5) , externally coaxial around an axis (A) to said hub (2) and supported in rotationally free motion on the hub, and a filtering unit (4) for transmitting the torque interposed between said hub (2) and said crown (3) and comprising a torsion spring (11) , a carrier (12) and a torque limiting joint (20) , said carrier (12) slidingly cooperating with respect to a head (7) integral with one of said hub (2) and said crown (3) , said torsion spring (11) being operationally interposed between said carrier (12) and said one of said hub (2) and said crown (3) and being provided with two ends cooperating in contact with respective spring holders (15) integral with said carrier (12) and said one of said hub (2) and said crown (3) , said torque limiting joint (20) being interference coupled on one surface (3, f) of the other of said crown (3) and said hub (2) , said torque limiting joint (20) comprising an open-ring strip spring (21) and being configured to slide with respectto said surface (3, f) when the torque transmitted between said crown (3) and said hub (2) reaches a predetermined level , said pulley (1) comprising a first and a second rolling support (6' , 6' ’ ) , of the same type, respectively operationally interposed between said head element (7) and said hub ( 2 ) , wherein said hub (2) comprises a main body (2a) extending along said axis (A) and a flanged portion (2b) , said flanged portion (2b) cooperating with said torsion spring (11) on one side and on the opposite side axially supporting said second rolling support (6' ' ) .2.- The pulley according to claim 1, wherein said surface (3, f) is made on said crown (3) , said carrier (12) slides with respect to said hub (2) and said spring (11) is operationally interposed between said carrier (12) and said hub (2) .3.- The pulley according to claim 1 or 2, wherein said rolling supports (6' , 6' ’ ) each comprise a ball bearing.4.- The pulley according to one of the previous claims, wherein said head (7) comprises an annular portion (7 ’ ) and a radial portion (7, f) , said radial portion (7, f) slidingly cooperating with said carrier (12) on one side and on the opposite side axially supporting said first rolling support (6' ) .5.- The pulley according to one of the previous claims, wherein said first and second rolling supports (6' , 6' ’ ) are placed on opposite sides of said pulley (1) along said axis (A) .6.- The pulley according to one of the previous claims, wherein said head (7) defines at least one projection (16) configured to cooperate in contact with at least one projection (17) defined by said carrier (12) .7.- The pulley according to one of the previous claims, wherein said strip spring (21) defines at least one projection (25) configured to cooperate in contact with at least one projection (18) defined by said carrier (12) .8.- The pulley according to one of claims 1 to 6, wherein said strip spring (21) defines at least one projection (25) configured to cooperate in contact within a seat (19) defined by a projection (18) defined by said carrier ( 12 ) .9.- The pulley according to one of the previous claims, wherein said torque limiting joint (20) comprises an actuator element (28) housed in a space (22) delimited circumferentially between two ends (21' , 21' ' ) of said strip spring (21) .10.- The pulley according to claim 9, 7 or 8, wherein said actuator element is a metal lever (28) adapted to cooperate in contact with said projection (18) or withinsaid seat (19) of said projection (18) .11.- The pulley according to one of the previous claims, wherein said pulley (1) comprises a damping ring (13) operationally interposed between said carrier (12) and said head (7) integral with said hub (2) , said damping ring (13) being configured to allow the sliding of said carrier (12) with respect to said head (7)12.- The pulley according to claim 11, wherein said damping ring (13) comprises a portion (13' ) radially interposed between said crown (3) and said carrier (12) and a portion ( 13 ’ ’ ) interposed between said carrier (12) and said head (7) integral with said hub (2) .13.- The pulley according to one of the previous claims, wherein said other of said crown (3) and said hub (2) defines a portion (23) machined superficially on said internal surface (3, f) , said strip spring (21) cooperating in contact with said portion (23) , said surface machining increasing the friction between said strip spring (21) and said other of said crown (3) and said hub (2) .

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