Improved filtering pulley

Abstract

Filtering pulley (1) for an accessory transmission of an internal combustion engine, comprising a hub (2), a crown (3) and a torque transmission filtering unit (4) interposed between the hub (2) and the crown (3) and comprising a torsion spring (21), a carrier (22) and a torque limiting joint (25), the torque limiting joint (25) comprising a band spring (26), having an open ring shape, and being configured to slide on the crown or on the hub (3, 2) when a given torque is reached.

Description

[0001] "IMPROVED FILTERING PULLEY"

[0002] Cross-Reference to Related Applications

[0003] This Patent Application claims priority from Italian Patent Application No . 102023000017880 filed on August 30 , 2023 , 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 finds a preferred, although not exclusive, application in the drive pulley of an alternator of an internal combustion engine . Reference will be made to said application in the following by way of example, it is clear however that the pulley of the invention can be used as a driving pulley connected to the crankshaft or as a driven pulley for driving any other accessory of the engine, for example a reversible electric machine with generator and motor function .

[0007] State of the Known Art

[0008] In motor vehicles, the use of a filtering pulley for driving the alternator by means of the accessory transmission belt is known .

[0009] Said pulley comprises a hub suitable to be connected to the alternator rotor, an annular crown provided with a profile suitable for cooperating with the belt and a filtering unit interposed between the hub and the crown of the pulley to avoid subj ecting the belt to dynamic overloads in the presence of torsional vibrations of the crankshaft or rapid variations in the speed of the engine . 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 .

[0010] Since the alternator has a relatively high equivalent inertia and tends to drive the pulley in the presence of instantaneous reductions in the speed of the crankshaft, it is known to incorporate a free wheel in the filtering unit suitable for unidirectionally transmitting the motion of the crown to the hub (normal operating condition) but for decoupling the hub from the crown in the event of torque reversal .

[0011] The introduction of start-stop systems in which a reversible electric machine is used as a starter motor or alternator, depending on the operating conditions, makes it impossible to use a free wheel filtering pulley because the latter would decouple the electric machine, acting as a driving element, from the belt transmission .

[0012] To solve this problem, solutions have been proposed wherein the filtering unit comprises a spring attached at the ends thereof to respective elements coupled to the hub and to the pulley, respectively, with a relative freedom of rotation of a given amplitude .

[0013] An example of a known solution to said problem is illustrated in WO 2015 / 198277 Al . However, said solution is not yet sufficiently optimised to guarantee the desired technical performance especially in the case of high torque to be transmitted, for example for heavy vehicles . There is therefore a need to provide a filtering pulley that can be used both in a start-stop system and in a conventional transmission system, which allows to solve the problems of the known filtering pulleys described above .

[0014] Another obj ect of the present invention is to provide a filtering pulley, which is compact and inexpensive to produce .

[0015] Summary of the Invention

[0016] The above obj ect is achieved by a pulley as claimed in the appended independent claims .

[0017] Further preferred embodiments of the invention are made according to the dependent claims or claims connected to the above-mentioned independent claims .

[0018] Brief Description of the Drawings

[0019] For a better understanding of the present invention, a preferred embodiment is described in the following, by way of non-limiting example and with reference to the attached drawings wherein :

[0020] • Figure 1 is a longitudinal sectional view of a pulley according to the invention;

[0021] • Figures 2A-2B are exploded perspective views of the pulley of Figure 1 ; and

[0022] • Figures 3 and 4 are perspective views, respectively from different angles, of the pulley of Figure 1 with parts removed for clarity during two different operating conditions .

[0023] Detailed Description of the Invention 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 torque transmission filtering unit 4 operatively interposed between the hub 2 and the crown 3 . The hub 2 and the crown 3 are coaxial around a longitudinal axis A.

[0024] The hub 2 is suitable 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 with the function of alternator and starter motor in a start-stop system.

[0025] In particular, the hub 2 comprises a first portion 2 ' and a second portion 2 ' ' rigidly connected to one another .

[0026] In detail, the first portion 2 ' is configured to be coupled to the aforementioned shaft and comprises a cylindrical portion 4 coaxial to the axis A and a radial portion 5 extending from one end of the cylindrical portion radially with respect to the axis A coupled with the second portion 2 ' ’ . The radial portion 5 advantageously defines a seat 6, annular shaped, configured to allow the housing of a part of the second portion 2 ’ ’ so as to allow the fixing thereof to the first portion 2 ’ as described in the following .

[0027] The second portion 2 ’ ’ has a "mushroom- like" shape comprising a cylindrical portion 7 sized so as to fit into the seat 6 of the aforementioned radial portion 5 and cooperate by means of a mechanical coupling with the same so as to fix the first and second portions 2 ’ , 2 ’ ’ together such as a key coupling or a friction coupling . The second portion 2 ' ' further comprises a flanged portion 8 extending from the cylindrical portion 7 and defining a "mushroomlike" profile delimiting an annular seat 9 as described in the following .

[0028] In particular, the flanged portion 8 is provided with a first radial wall 8a extending from one end, opposite to the first portion 2 ' , radially with respect to the axis A, a cylindrical wall 8b extending starting from the first radial wall 8a and moving away from the same parallel to the axis A, a second radial wall 8c extending on the opposite side of the first radial wall 8a starting from the cylindrical wall 8b and a second cylindrical wall 8e extending starting from the second radial wall 8c towards the first radial wall 8a and parallel to the first cylindrical wall 8b .

[0029] According to the above-described shape of the flange 8 , the annular seat 9 is radially delimited by the first and second cylindrical walls 8b, 8d and axially delimited by the second radial wall 8c, on one side along the direction of the axis A and open on the other .

[0030] The crown 3 essentially comprises a first and a second annular portion 3a, 3b . Advantageously, the first annular portion 3a has a diameter smaller than the second annular portion 3b and is connected to the same by means of a radial portion 3c .

[0031] Advantageously, the first annular portion 3a radially surrounds the first portion 2 ' of the hub 2 whereas the second annular portion 3b radially surrounds the second portion 2 ' ' of the hub 2. In particular, the first annular portion 3a defines a profile 3 ' with multiple grooves suitable for cooperating with a poly-V belt (of which a section is schematically shown in Figure 1 ) .

[0032] The crown 3 is supported on the hub 2 by means of support means configured to allow free rotation between hub 2 and crown 3.

[0033] In particular, the pulley 1 comprises a rolling bearing 11 , for example a pair of ball bearings, radially interposed between the first portion of the crown 3 and the first portion 2 ’ of the hub 2 . On the other hand, the pulley 1 comprises a sliding bearing 12 , for example a ring made of a low friction material, radially interposed between the second portion 3' ’ of the crown 3 and the second portion

[0034] 2 ' ' of the hub 2.

[0035] In detail, the second portion 3' ' substantially comprises a cylindrical wall connected by means of the radial portion 3c to the first portion 3a and defining a space 13 radially delimited by the aforementioned cylindrical wall and by the second portion 2 ' ’ of the hub 2 and axially closed by the flanged portion 5 of the first portion 2 ’ of the hub 2 on one side and by a cover 14 on the opposite side, which is housed in an opening defined by the second portion 3b of the crown 3 .

[0036] The filtering unit 4 is housed in the space 13 and essentially comprises a torsion spring 21 , a spring-holder element 22 , hereinafter called carrier, cooperating with one end of the spring 21 and a damping ring 23 axially interposed between the carrier 21 , the hub 2 and the pulley 3. In particular, the carrier 22 cooperates in sliding contact with the radial portion 5 of the hub 2 and with the radial portion 3c in the axial direction and with the inner surface of the cylindrical wall 3b .

[0037] As better shown in Figures 2A, 2B, preferably, the carrier 12 has an annular shape and defines an annular wall 22 ' coaxial with the axis A and a radial wall 22 ' ’ extending radially towards the axis A starting from an axial edge of the annular portion 22 ’ .

[0038] Similarly, the damping element 23 comprises an annular wall 23 ' coaxial with the axis A and a radial wall 23 ' ’ extending radially towards the axis A starting from an axial edge of the annular portion 23' so as to cooperate in contact with the annular and radial walls 22 ' , 22 ' ’ . In particular, the damping element 23 is coupled, by friction or by shape coupling, to the carrier 22 and is therefore integral with the same around the axis A. Preferably it is made of a polymeric material .

[0039] As stated, the aforementioned radial wall 22 ' ' while on a first side cooperates by sliding with the aforementioned walls of the crown 3 and the flange 4 , on a second side axially opposite to the previous one defines an axial protrusion 22 ' ' ' configured to cooperate with the spring 25.

[0040] The annular wall 22 ' defines, furthermore, a pair of inner radial proj ections 24 advantageously made opposite to one another circumferentially along the axis A and configured to cooperate with protrusions 5' extending axially starting from the radial portion 5 of the hub 2 and also arranged opposite circumferentially around the axis A.

[0041] Said inner radial proj ections 24 are configured to cooperate with the protrusions 5' so as to be selectively placed in contact as a function of the rotation of the carrier 22 around the axis A, thus limiting the free rotation with respect to the hub 2 .

[0042] The spring 21 is preferably a helical spring having a circular section wire and comprising a plurality of coils winding around the axis A between the carrier 22 and the flanged portion 8 of the second portion 2 ' ' of the hub 2 . As stated above, an end portion of the spring 21 cooperates in contact with the axial protrusion 22 ' ' ' acting as a spring holder while the opposite end cooperates in contact with a respective spring holder, not shown, advantageously housed in the annular seat 9.

[0043] In detail, the spring 21 has dimensions at least equal to the diameter of the multi-V profile 3' and in particular substantially corresponding to the diameter of the first portion 3a of the crown 3.

[0044] As shown in Figures 2B, 3 and 4 , the filtering unit further comprises a torque limiting j oint 25 essentially comprising a band spring 26 housed in the space 13 and configured to simultaneously perform the free wheel function in both directions of relative rotation between crown 3 and hub 2 . Advantageously, said free wheel effect is provided at different torque levels transmittable between hub 2 and crown 3 in one direction with respect to the other .

[0045] In particular, the torque limiting j oint 25 is sized to cooperate in contact with the hub 2 and the carrier 22 to decouple the crown 3. In particular, the limiting j oint 25 is housed in the space 13 in contact with an inner surface of the crown 3. Advantageously in said contact portion the inner surface of the crown 3 comprises a machined area so as to increase the friction between the band spring 26 and the crown 3. In particular, the area is machined to define a grooved / wavy surface, of the "ribbed" type, of dimensions suitable for allowing a given friction between the band spring 26 and the crown 3 .

[0046] In greater detail, the band spring 26 has the shape of a substantially open ring with two ends 26' , 26' ’ delimiting a space 27 between the same . The band spring 21 has a substantially constant axial dimension throughout its circumferential extension and has a preferably rectangular section .

[0047] However, one 26' of the two end portions 26' ' defines at least one proj ection 31 , 32 . In particular, according to the embodiment described,

[0048] - a first proj ection 31 extends in a circumferential direction starting from the end portion 26' towards the opposite end portion 26' ’ inside the space 27 ; and

[0049] - a second proj ection 32 extends axially along the axis A from an axial edge of the band spring 26 towards the carrier 22 .

[0050] The second proj ection 31 is axially sized to cooperate in contact in a circumferential direction with the carrier 12 , in particular on the inside, axially, of an axial seat 33 obtained on the edge of the annular wall 22’ extending along the axis A axially and circumferentially around the same for a given value, advantageously less than 90 ° , in particular less than 45° .

[0051] Consequently, the axial seat 33 is circumferentially delimited by a pair of circumferential edges / walls .

[0052] The torque limiting j oint 20 comprises , furthermore, an actuator element 34 housed in the space 28 and configured to cooperate in contact with the carrier 22 inside the axial seat 33 to increase or decrease the opening of the band spring 25 when the actuator element acts in contact with the aforementioned circumferential edges / walls acting as end stops .

[0053] Advantageously, the actuator element 34 comprises a metal lever housed in the space 28 and circumferentially interposed between the end portions 26' , 26' ’ of the band spring 26 and configured to cooperate in contact with the proj ection 31 and the end portion 26' ' , circumferentially, and extending in an axial direction to cooperate in contact circumferentially within the axial seat 33.

[0054] In particular, the lever of the actuator element 34 has a trapezoidal shape where the base of the trapezoidal shape is in a circumferential direction and the thickness in a radial direction with respect to the axis A. In particular, therefore, the lever comprises a central portion having a substantially rectangular shape and a pair of tapered lateral portions that are advantageously equal to one another .

[0055] Preferably, the angle of inclination of the lateral portions with respect to the central portion is comprised between 20 ° and 40 ° , advantageously 30 ° . The operation of the embodiment of the pulley 1 according to the invention described above is as follows .

[0056] In normal conditions, namely, when the crown 3 driven by the belt 4 drives the hub 2 and therefore tends to overtake the same ("drive mode") , the band spring 26 rotates integrally with the crown 3 and the hub 2 is resistant .

[0057] Imagining a starting condition in which one of the lateral portions of the actuator 34 is in contact with a end stop wall of the axial seat 33, the band spring 26 will tend to move clockwise with respect to the axis A, driven by the crown 3. The actuator 34 moves inside the seat 18 ' until ( Figure 3 ) the proj ection 32 of the spring 26 comes into contact with the proj ection of the opposite end stop of the axial seat 33. Starting from said condition, the actuator 34 is inclined ( Figure 4 ) as it is pushed tangentially between the portions 26' , 26' ’ by the thrust between the proj ection 31 and the aforementioned end stop . In this way, the opening increases, thus increasing the adhesion between the latter and the inner surface of the crown 3. In this way, the spring 21 is torsionally loaded and transmits torque to the hub 2 being attached at the opposite flanged portion 8 . If the torque transmitted by the crown 3 continues to increase, at a given point the band spring 26 slips with respect to the inner surface of the crown 3, lacking the necessary adhesion and thus decoupling the crown 3 and the hub 2 .

[0058] In the case in which, instead, the hub 2 tends to overtake the crown 3 ("overrunning") , the spring 26 rotates together with the crown 3 and is resistant with respect to the hub 2 . Assuming the decoupling condition described above, the crown 3 will tend to rotate counterclockwise with respect to the hub 2 , thus decoupling the actuator lever 34 from the end stop defined by the seat 33. In said condition, the spring 11 will tend to unload and the band spring 26, carried by the crown 3, will continue to rotate counterclockwise until the proj ection 32 touches the opposite end stop of the seat 33, thus tending to close the band spring 26 which will easily slip with respect to the inner surface of the crown 3, thus decoupling the crown 3 and the hub 2 .

[0059] If the actuator 34 is not provided, the operation is similar and in the driving torque condition the coupling occurs directly between the proj ection 32 and the end stops of the seat 33.

[0060] From the foregoing, the advantages of a pulley 1 according to the invention are evident .

[0061] Compared to the known solutions that provide for the use of a free wheel, the present invention provided with a torque limiting j oint 20 allows to obtain a bidirectional coupling between hub and pulley, at least within a given torque range, thus making it possible to use the pulley in start-stop systems .

[0062] Furthermore, compared to the described solutions, the housing of the torsional spring 21 allows to obtain high transmission torque, thus making the pulley usable even in heavy applications .

[0063] In particular, the dedicated housing in a space having dimensions larger than the connecting profile with the belt allows to use a torsional spring with a larger diameter and reduced axial dimension, thus obtaining a high torque transmission in a substantially reduced space .

[0064] Furthermore, the trapezoidal shape of the actuator lever 34 is particularly optimized in order to guarantee the opening of the spring 26 and at the same time sufficient structural resistance .

[0065] Finally, it is clear that modifications and alternatives can be made to the pulley 1 according to the present invention, which however do not go beyond the scope of protection defined by the claims .

[0066] In particular, the spring 26 could be coupled to the hub 2 instead of the crown 3.

[0067] The actuator element 34 , as mentioned, can be omitted in the case in which the adhesion between the spring 26 and the surface of the crown 3 (or of the hub 2 ) in the "drive mode" is sufficient to transmit the required torque .

[0068] Clearly, the angular values of the seat 34 can vary depending on the need for vehicle transmission .

[0069] The pulley can be used as a drive pulley on the crankshaft instead of on the alternator and can also be used on a conventional alternator or on any other accessory.

Claims

CLAIMS1.- A filtering pulley (1) for an accessory transmission of an internal combustion engine, comprising a hub (2) , an annular crown (3) provided with a profile (3' ) configured to cooperate with a transmission belt (V) , externally coaxial around an axis (A) to said hub (2) and supported in rotationally free manner on the hub itself, and a torque transmission filtering unit (4) interposed between said hub (2) and said crown (3) and comprising a torsion spring (21) , a carrier (22) and a torque limiting joint (25), said crown (3) comprising a first annular portion (3a) and a second annular portion (3b) , said first annular portion (3a) defining said profile (3' ) , said second annular portion (3b) defining with said hub (2) a space (13) configured to house said filtering unit (4) , said second annular portion (3b) having a diameter larger than said first annular portion (3a) so that said torsion spring (21) has a diameter larger than said coupling profile (3' ) , wherein said hub comprises a first portion (2' ) and a second portion (2'') said first portion (2') being configured to be connected to said rotating shaft, said second portion (2'' ) defining said space (13) with said second annular portion (2b) , wherein said second portion (2, f) defines an annular seat (9) configured to support a first end of said spring (21) and said carrier (22) is configured to support a second end of said spring (21) , said carrier (22) cooperating by sliding with respect to a portion (5) integral with one of said first and second portions (2', 2'') .2.- The pulley according to claim 1, wherein said first annular portion (3a) is supported on said first portion (2') by means of rolling support means (11) .3.- The pulley according to claim 1 or 2, wherein said second annular portion (3b) is supported on said second portion {2' ' ) by sliding support means (12) .4.- The pulley according to one of the preceding claims, wherein said carrier (22) comprises a radial wall {22’’) cooperating by sliding with said portion (5) , said radial wall {22’’) defining at least one projection (24) extending radially internally of said radial wall {22’’) and configured to cooperate in contact with at least one protuberance (5' ) extending axially from said portion (5) .5.- The pulley according to claim 4, comprising a pair of projections (24) and a pair of protuberances (5') angularly opposite to one another with respect to the axis (A) .6.- The pulley according to one of the preceding claims, wherein said carrier (22) comprises an annular wall {22’) defining an axial seat (33) said torque limiting joint (25) comprising a band spring (26) provided with a first and a second end (26', 26'') , at least one of said first and second ends (26', 26' ’ ) defining a projection (32) configured to cooperate selectively in contact with one of the circumferential edges of said axial seat (33) .7.- The pulley according to claim 6, wherein said torque limiting joint (25) comprises an actuator element (34) housed in a circumferentially delimited space (27) between said first and second ends (26', 26'') of said band spring (26) , said actuator element (34) being sized in an axial direction to cooperate in contact with one of the circumferential edges of said axial seat (33) .8.- The pulley according to claim 7, wherein said actuator element (34) is a metal lever suitable to expand said spring (26) under the thrust of said circumferential edge of said axial seat (33) .9.- The pulley according to claim 7 or 8, wherein one of said ends (26', 26'') defines a circumferential protuberance (31) extending into said space (22) and configured to cooperate in contact with said actuator element (34) .10.- The pulley according to one of the claims from 8 to 9, wherein said actuator element (34) has a trapezoidal section, where the base of said section is in the circumferential direction and the thickness of said actuator element (34) is in the radial direction.11.- The pulley according to one of the preceding claims, further comprising a damping ring (23) operatively interposed between said carrier (22) and said portion (5) integral with said hub (2) , said damping ring (23) being configured to facilitate the sliding of said carrier (22) with respect to said portion (5) .12.- The pulley according to one of the preceding claims, comprising a cover (14) carried by said crown (3) and configured to insulate said space (13) from the external environment.

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