WO2011141799A1

WO2011141799A1 - Damper pulley assembly

Info

Publication number: WO2011141799A1
Application number: PCT/IB2011/001002
Authority: WO
Inventors: Luca Gozzellino; Gianluca Cariccia; Tommaso Di Giacomo
Original assignee: Dayco Europe S.R.L.
Priority date: 2010-05-11
Filing date: 2011-05-11
Publication date: 2011-11-17
Also published as: IT1399993B1; ITTO20100394A1

Abstract

A pulley assembly (1; 50) comprising a hub (2; 51), a pulley (5; 53) supported with respect to the hub (2; 51) by means of a rolling bearing (21) and defining a profiled surface suitable for making contact with a flexible endless element, a unidirectional coupling (13, 28, 19; 65, 76, 80) to selectively couple the hub (2; 51) to the pulley (1; 50), control means (25; 78) to control the unidirectional coupling (13, 28, 19; 65, 79, 80) and an elastic torsional assembly (5; 54) arranged in series between the hub (2; 51) and the pulley (5; 53).

Description

"DAMPER PULLEY ASSEMBLY"

TECHNICAL FIELD

The present invention relates to an improved pulley assembly comprising a coupling, preferably for driving a flexible endless element, such as an accessory drive belt of a motor vehicle.

BACKGROUND ART

Recent regulations have imposed increasingly stricter emission limits for newly manufactured motor vehicles. In particular, carbon dioxide is a product of combustion that is monitored because it causes the greenhouse effect. In order to reduce carbon dioxide emissions, fuel consumption can be reduced and, in particular, energy losses related to friction-induced dissipation can be reduced, so as to render the internal combustion engine more efficient. For example, a control strategy for an internal combustion engine called start-stop is known, which switches the engine off in certain predetermined situations, such as when stopping at traffic lights for example. These predetermined situations normally correspond to the engine's idle speed so as to reduce both fuel consumption and noxious emissions, such as non- stoichiometric nitrogen oxides, the emissions of which are greater when the engine is idling.

Another method for reducing fuel consumption is that of making an accessory drive that is configured to disengage one or more accessories if these are not used by the user. For this purpose, the drive comprises a pulley that can be disengaged by means of a control device connected to the engine's control unit. For example, the pulley is connected to the crankshaft and comprises an electromagnetic coupling. When the electromagnetic coupling is engaged, the pulley drives the belt and all the accessories connected to the belt, such as the compressor of an air conditioning system for example, or an alternator or a reversible electric machine. When the coupling is disengaged, the belt is rotationally uncoupled from the crankshaft and remains stationary even when the vehicle moves .

However, the operation of engaging and disengaging the coupling when the crankshaft is running at high revs, for example when the vehicle is driven on the motorway, requires a lot of energy to be absorbed, which can cause noise and wear and so render this solution advantageous from the emission reduction standpoint, but disadvantageous from the vehicle comfort standpoint.

DISCLOSURE OF INVENTION

The object of the present invention is to make a pulley assembly comprising an electromagnetic coupling devoid of the above-specified drawback.

The object of the present invention is achieved by a pulley assembly comprising a coupling according to claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, it will be further described with reference to the attached Figures, in which:

Figure 1 shows a section of a pulley assembly comprising a coupling according to the present invention; and

Figure 2 shows a section of a second embodiment of the present invention .

BEST MODE FOR CARRYING OUT THE INVENTION

In Figure 1, reference numeral 1 indicates, as a whole, a pulley assembly comprising a hub 2 suitable for being connected to a rotating output shaft, for example to the crankshaft of an internal combustion engine, a dynamic torsional dampener 3, a pulley 4 idle with respect to the hub 2, an elastic torsional assembly 5 to connect the hub 2 to the pulley 4 and an electromagnetic coupling 6 to selectively connect the pulley 4 to the hub 2 by means of the elastic torsional assembly 5.

In particular, the torsional dampener 3 comprises a support rigidly connected to the hub 2, a inertia ring 7 and an elastic element 8 to connect the inertia ring 7 to the support. The support comprises, preferably in one piece, a connection portion 9 axis-symmetric with respect an axis A and directly assembled on hub 2, a web 10 extending radially outwards from the connection portion 9 and a cylindrical wall 11 extending axially from the periphery of the web 10. In particular, the cylindrical wall 11 defines a rest surface for the elastic element 8 and preferably has the same axial dimension as both the inertia ring 7 and the elastic element 8. Advantageously, the elastic element 8 comprises a ring of an elastomeric material vulcanized between the cylindrical wall 11 and the inertia ring 7.

The connection portion 9 and the cylindrical wall 11 define an annular cavity that surrounds the elastic torsional assembly 5 in a radial direction and partially houses it in an axial direction. In particular, in the present description and in the claims, the term "surround" means that the surrounded element intersects the axial space occupied by the surrounding element and that further structural and non-structural elements can be inserted between the surrounded element and the surrounding one along the radial direction. In addition, the elastic torsional assembly 5 comprises a spiral spring 12 having an end portion rigidly connected to the connection portion 9, and an annular element 13. The annular element 13 is rigidly connected to the other end portion of the spiral spring 12 and has an axial and radial position respectively defined by the web 10 and the cylindrical wall 11. In particular, the annular element 13 defines a C-shaped cross- section open on the part opposite to the web 10 and comprises an inner cylindrical wall 14 preferably connected to the last coil of the spiral spring 12 by interference, a back wall 15 extending radially outwards from the inner cylindrical wall 14 and an outer cylindrical wall 16 axially leaving the perimeter of the back wall 15. In use, the annular element 13 rotates with respect to the web 10 and to avoid wear and to dampen torsional oscillations, the pulley assembly 1 comprises a friction disc 17 inserted between the back wall 15 and the web 10 and a friction ring 18 inserted between outer cylindrical wall 16 and cylindrical wall 11. Arranged on the opposite side of the torsional dampener 3 with respect to the elastic torsional assembly 5, the pulley 4 comprises a crown 19 defining a surface, preferably grooved, suitable for making contact with a belt of a belt drive, preferably an accessory drive, a web 20 extending from the crown 19 towards axis A and a rolling bearing 21 for radially supporting the web 20 and the crown 19 on the hub 2. Advantageously, the web 20 is arranged in an axially median position of the crown 19 so as to delimit an inner cylindrical surface 22 and a cavity 23 on axially opposed sides. The inner cylindrical surface 22 faces towards the elastic torsional assembly 5 and is at least partially overlapping in an axial direction to the hub 2 and/or to the connection portion 9. The cavity 23 is annular and is delimited at the bottom by a tubular wall 24 that rests on the rolling bearing 21 and preferably defines a single piece with web 20 and the crown 19. In this way, the rolling bearing 21 is at least partially surrounded by the crown 19 such that the load of the latter can be transferred to the bearing itself with little or no misalignment .

The cavity of the annular element 13 and cavity 23 surround the electromagnetic coupling 6 in the radial direction and at least partially houses it in the axial direction. The electromagnetic coupling 6 comprises a fixed coil 25, connected to a wall of an internal combustion engine for example, an axially moveable anchor 26 arranged in an axial direction between the web 20 and the elastic torsional assembly 5, and a ribbon spring 27 connected between the anchor 26 and the pulley 4. In particular, the anchor 26 comprises a profiled disc 29 inserted axially between the spiral spring 12 and the web 20, a cylindrical support wall 30 leaving the perimeter of the profiled disc 29 inside the cavity of the annular element 13 and an end wall 31 radially leaving an end portion of the support wall 30. The end wall 31 makes contact and frictionally cooperates with the back wall 15 thanks to the action of a spring 32, a cup spring for example, inserted between the web 20 and the disc 29. In addition, the end wall 31 is rigidly connected to an end portion of the ribbon spring 27 while the other end portion is rigidly connected to the pulley 3, advantageously to the web 20. The spring 32 is configured to radially support the anchor 26. Preferably, the spring 32 is mounted between two annular shoulders respectively defined on the disc 29 and on the web 20 and supporting the inner edge and outer edge of the spring 32.

Figure 2 shows a pulley assembly 50 according to a further embodiment of the present invention. The pulley assembly 50 comprises a hub 51, a torsional dampener 52, a pulley 53 idle with respect to the hub 51, an elastic torsional assembly 54 to connect the hub 51 to the pulley 53 and an electromagnetic coupling 55 to selectively connect the pulley 53 to the hub 51 by means of the elastic torsional assembly 54.

In particular, the torsional dampener 52 comprises a support rigidly connected to the hub 51, a inertia ring 56 and an elastic element 57 to connect the inertia ring 56 to the support. The support comprises, preferably in one piece, a connection portion 58 axially symmetric with respect to the longitudinal centerline axis B of the hub 51 and a web 59 radially leaving the connection portion 58. The elastic element 57 is fixed on the perimeter of the web 59 and, advantageously, comprises a ring of a vulcanized elastomeric material .

The connection portion 58 also defines a seat 60 to radially support the pulley 53. The pulley 53 comprises a crown 61 defining a work surface, a grooved one in this embodiment, suitable for making contact with the belt of a belt drive, a web 62 leaving an edge 63 of the crown 61 in an inclined manner towards web 59 and a rolling bearing 64 to radially support web 62 and the crown 61 on the seat 60. The pulley 63 also comprises a tubular wall 65 axially leaving web 62 and at least partially surrounded by the latter. The tubular wall 65 is mounted on the outer ring of the rolling bearing 64 and preferably defines a single piece with web 62 and the crown 61.

The elastic torsional assembly 54 is arranged on the axially opposite side of web 59 with respect to the rolling bearing 64. The elastic torsional assembly 54 comprises a spiral spring 66 having an end portion rigidly connected to the hub 51 and an annular unit 67 rigidly connected to the other end portion of the spiral spring 66 and having an axial and radial position respectively defined by respective flat and cylindrical surfaces of a shoulder 68 axially leaving the connection portion 58. In particular, the annular unit 67 is a shell comprising a first and a second element 69, and at least partially housing the spiral spring 66 in the radial direction and completely in the axial direction. The first element 69 is mounted on the shoulder 68, a ring 71 being inserted in the radial direction and a washer 72 in the axial direction to generate a damping effect and to avoid direct contact. Advantageously, the first element 69 comprises a tubular wall 73 mounted on the ring 71, a radial wall 74 leaving the tubular wall 73 and arranged to make contact with the washer 72, and a coupling wall 75 axially leaving the radial wall 74 on the opposite side from the tubular wall 73. The coupling wall 75 is rigidly connected to the last coil of the spiral spring 66 and to the second element 70 of the annular unit 67. In particular, the second element 70 of the annular unit 67 comprises a connection wall 76 rigidly connected to the coupling wall 75 and a radial wall 77 leaving from an edge of the connection wall 76 towards the hub 51. Advantageously, the last coil of the spiral spring 66 is connected with the coupling wall 75 and/or the connection wall 76 with the coupling wall 76 by radial interference. In addition, the radial wall 77 can have a size such as to approximate by defect to the size of the spiral spring 66 mounted in the first element 69 on the hub 51.

The electromagnetic coupling 55 is arranged between the annular unit 67 and the crown 61 in the radial direction and comprises a fixed coil 78, connected to a wall of a internal combustion engine for example, an axially moveable anchor 79 having a portion arranged in a radial direction between the elastic torsional assembly 54 and the coil 78, and a ribbon spring 80 connected between the anchor 79 and the pulley 63. In particular, the anchor 79 comprises a shoulder 81 selectively cooperating with the annular unit 67, the portion 82 inserted between the coil 78 and the elastic torsional assembly 54 and a ferromagnetic portion 83 directly facing the coil 78. Preferably, the anchor 79 is made in one piece starting from a sheet of ferromagnetic material and is located in the radial direction by means of a support bush 84 fixed on an inner surface of the crown 61. In addition, the anchor 79 is kept in contact with the annular unit 67, preferable through the shoulder 81, by means of a spring 85 radially inserted between the crown 61 and the anchor 79. In particular, the spring 85 is of the cup type and has an outer peripheral edge constrained between the web 62 and the head of the bush 84. An inner peripheral edge of the spring 85 instead makes contact with a ridge 86 of the anchor 79 so as to push the anchor 79 itself towards the web 62. Furthermore, the anchor 79 is mobile with axial travel being delimited on one side by a stop preferably defined by the spring 85 and by a stop defined by a ridge 87 leaving the bush 84 towards axis B on the other. In addition, the anchor 79 is radially supported by the pulley 53 through the bush 84.

The operation of the pulley assembly 1 is as follows.

When the coil 25 is not energized, the spring 32 exerts an axial action on the anchor 26 and the end wall 31 is pressed against an inner surface of the back wall 15 inside the 'C section of the annular element 13. In this way, the anchor 26 is rotationally integral with annular element 13 and is driven by the hub 2 through the spiral spring 12.

When the coil 25 is not energized and the hub is driven in rotation by the crankshaft, the anchor 26 tends to rotate thanks to the action of the spring 32, while the pulley 4 tends to remain stationary because it is mounted on the rolling bearing 21. The band spring 28 has a winding angle such that the relative speed between hub 2 and pulley 4 when the crankshaft turns in the direction of operation (normally clockwise in Europe) , tends to unwind the coils and increase their average radius . The increase in average radius causes contact with an inner cylindrical surface identified by the annular element 13, preferably by the cylindrical wall 1 and by the pulley 4, preferably by the crown 19, so as to define a unidirectional coupling, a unidirectional belt coupling in the present non-limitative description. The belt coupling of the pulley assembly 1 is such as to define a condition of rigid connection between the annular element 13 and the crown 19 when the coils unwind. Thus, the hub 2, pulley 4 and elastic torsional assembly 5 are arranged in series and, when the coil

25 is not energized, the hub 2 drives the pulley 4 through the action of the elastic torsional assembly 5. It is important to note that the force of friction that produces the coupling between the annular element 13 and the crown 19 is due to the action of the coils of the band spring 28 and is proportional to the transmitted torque. The spring 32 has a limited axial load and has the function of making the anchor 26 integral with the annular element 13.

If the pulley 4 tends to rotationally overtake the hub 2, the coils of the band spring 28 decrease in diameter until they angularly uncouple the pulley 4 with respect to the annular element 13. However, when the hub 2 returns to providing drive, the band spring 28 couples to the crown 19 and to the annular element 13 again. When the coil 25 is not energized, the pulley 4 preferably has limited angular travel with respect to the annular element 13 as the band spring 28 has the end portions respectively connected in a rigid manner to the pulley 4 and to the annular element 13. For example, an operating condition where the pulley 4 can overtake the hub 2 and the annular element 13 is represented by sharp braking of the crankshaft. The number of engine revs drops together with that of the hub 2 while, contrariwise, the inertia of the accessory drive continues to drive the crown 19 at a high angular speed through the belt. An operating condition where the pulley 4 can intermittently overtake the hub 2 is that of starting, during which strong irregularities in crankshaft rotation are associated with the inertia of the accessory drive .

The coil 25 can be energized following a command coming from a control unit of the internal combustion engine. In this case, the force of electromagnetic attraction exerted on the anchor

26 is greater than the load of the spring 32, so that the end wall 31 separates from the annular element 13. However, when the coil 25 is energized, the end portion of the band spring 28 connected to the anchor 26 is no longer driven in relative rotation by the annular element with respect to the pulley 4 and the coils decrease their diameter and separate from the annular element 13, so as to open the band coupling. In this operating condition, the hub 2 is driven by the crankshaft and the pulley 4, spring 32, anchor 26 and band spring 28 are rotationally disconnected from the engine shaft. Preferably, the coil 25 is energized to disconnect the accessories, such as the compressor of the air-conditioning system or a reversible electric machine for example, from the engine. The coil 25 is kept energized for all the time that the pulley 4 is rotationally disconnected with respect to the hub 2.

If the user and/or the control unit automatically activates the switching on of one of the accessories driven by the pulley assembly 1 while the internal combustion engine is running, the coil 25 is no longer energized and the action of the spring 32 pushes the anchor 26 against the annular element 13 again. This causes the band coupling to close and the rotational connection of the pulley 4 to the hub 2. The torque peaks and consequent oscillations are absorbed in an efficient manner by the spiral spring 12 , which functions as a torque absorber and reduces the loads on the belt of the accessory drive. In particular, the damping of the elastic torsional assembly 5 is due both to the spiral spring 12 and to the friction elements 17 and 18, which dissipate part of the kinetic energy of the oscillations induced by the closure of the band coupling.

In addition, under all working conditions of the pulley assembly 1, the dynamic torsional dampener 3 dampens the torsional vibrations of the crankshaft and its action contributes to further reducing stress on the belt of the accessory drive. In particular, the dynamic torsional dampener is mounted in parallel with the elastic torsional assembly 5, with respect to the hub 2.

The operation of pulley assembly 50 is similar to that of pulley assembly 1. Due to the arrangement and configuration of the elastic torsional assembly 54, the band spring 80 and the anchor 79, the band coupling is closed when the coils of the band spring 80 reduce their diameter and make simultaneous contact with an outer cylindrical surface defined by the pulley 53, in particular by the tubular wall 65 and by the annular unit 67, and in particular by the connection wall 76. In addition, the friction-based damping function is performed by the ring 71 and the washer 72. Finally, the selective contact between the anchor 79 and the annular unit 67 is effected between the shoulder 81 and the radial wall 77.

In each embodiment, it has been checked that the operation of closing the band coupling can be carried out within a maximum angular speed limit of the hub 2, 51. In consequence, the engine's control unit implements a function that monitors the angular speed of the hub 2, 51, via the number of crankshaft revs for example, compares this value with the maximum angular speed limit, possibly programmed by an operation on the control unit or by a control that can be operated by the driver of the vehicle, and automatically controls the band coupling if the angular speed of the hub reaches the maximum value programmed in the control unit. In particular, if the accessories are not used, the control unit in any case closes the coupling and suspends the energizing of the coil 25, 78. Instead, if the accessories are already in use, any control or routine that requires the coil to be energized is disabled until the speed of the hub 2, 51 falls below the predetermined maximum angular speed limit. In this way, when the coupling is closed, the inertial load of the accessories has a small value so as not to excessively stress the elastic torsional assembly 5, 54. It has been verified that the angular speed limit is, for example, below 3000 revs and, more in general, below a predetermined threshold value.

The advantages of the pulley assembly 1, 50 according to the present invention are the following.

The elastic torsional assembly 5, 54 has, on average, reduced rigidity to absorb the stress generated when the differences in speed between hub and pulley are high, but still below the maximum angular speed of the crankshaft of the internal combustion engine. Beyond the above-mentioned limit, noise and stress due to the coupling are too high. The damping of the torsional oscillations due to the torsional assembly 5, 54 results in a drop in tension peaks on the belt of the accessory drive and improves the latter's operating conditions .

The spring 32, 85 reduces electrical energy consumption because the operating conditions where the band coupling is closed for driving the accessory drive are greater.

The band coupling, the elastic torsional assembly 5, 54 and the pulley 4, 53 are configured so that the pulley assembly 1, 50 is as compact as possible, both in the axial direction and in the radial direction.

When the rolling bearing 21 is surrounded by the crown 19, the reverse moments acting on the bearing are little or null. When the annular unit 67 at least partially encloses the spiral spring 66 in the axial direction as well, the latter is protected from debris in a substantially closed volume.

When the coil 78 is directly facing the ferromagnetic portion 83, namely when there are no further elements inserted between coil and electromagnetic portion, the coil 78 can have a small size because relatively low energy levels are required for moving the anchor 79.

Finally, it is understood that changes or modifications may be made to the pulley assemblies 1, 50 described and illustrated herein without departing from the scope of protection, as specified in the attached claims.

Advantageously, according to any embodiment of the present invention, the elastic torsional assembly 5, 54 is in series with the respective pulley 4, 53 and can be above (as previously described) or below the band coupling with respect to the hub 2, 51. In general, the pulley assembly 1, 50 can also be applied to an output shaft of any device, such as an accessory for example and not just the crankshaft. In this case, the pulley assembly is not provided with the dynamic torsional dampener. At least one of the two end portions of the band spring 28, 80 could slide in a groove defined by the respective support element. This groove has a variable radius in the tangential direction to simplify the operation of closing and/or opening the coupling.

Depending on the applications, the elastic function of the band spring 28, 80 could be performed by a ring of an elastomeric material.

Claims

1. A pulley assembly (1; 50) comprising a hub (2; 51), a pulley (5; 53) supported with respect to said hub (2; 51) by means of a rolling bearing (21) and defining a profiled surface adapted to come into contact with a flexible endless element, a unidirectional coupling (13, 28, 19; 65, 76, 80) to angularly couple said hub (2; 51) to said pulley (1; 50) in a first relative direction of rotation and to angularly uncouple said hub (2; 51) and said pulley (1; 50) in a second relative direction of rotation, and an elastic torsional assembly (5; 54) arranged between said hub (2; 51) and said pulley (5; 53) to transfer a load through said unidirectional coupling (13, 28, 19; 65, 76, 80), characterised by comprising control means (25; 78) to control said unidirectional coupling (13, 28, 19; 65, 76, 80) between a first position in which said hub (2; 51) and said pulley (5; 53) are angularly coupled by means of said directional coupling (13, 28, 19; 65, 76, 80) in said first direction of rotation and a second position in which said hub (2; 51) and said pulley (5; 53) are angularly uncoupled in said first direction of rotation.

2. The pulley assembly according to claim 1, characterised by comprising a passive friction dampener (17, 18; 71, 72) cooperating with said pulley (4; 53) to dampen the angular oscillations of said pulley (5; 53) when said unidirectional coupling (13, 28, 19; 65, 79, 80) is closed by means of said control means (25; 78) .

3 The pulley assembly according to any of the preceding claims, characterised in that said unidirectional coupling (13, 28, 19; 65, 76, 80) comprises mobile equipment (26, 28; 79, 80) operated by said control means (25, 78) and in that said mobile equipment (13, 28; 79, 80) is rotationally integral with said pulley (4; 53) when said unidirectional coupling (13, 28, 19; 65, 79, 80) is open.

4 The pulley assembly according to any of the preceding claims, characterised in that said unidirectional coupling (13, 28, 19; 65, 76, 80) is a band coupling.

5 The pulley assembly according to any of the preceding claims, characterised in that said pulley assembly (4) comprises a rolling bearing (21) and in that said rolling bearing (21) is at least partially surrounded by said profiled surface.

6. The pulley assembly according to any of the preceding claims, characterised in that said elastic torsional assembly (5; 54) comprises a spiral spring (12; 66) having a first end portion angularly fixed with respect to said hub (2; 51) and by comprising an annular unit (13; 67) angularly fixed with respect to a second end portion of the said spiral spring (12; 66) and surrounding said spiral spring (12; 66) so as to cooperate with said unidirectional coupling (13, 28, 19; 65, 79, 80) .

7. The pulley assembly according to claim 6, characterised in that said annular unit (13) at least partially houses said unidirectional coupling (13, 28, 19) .

8. The pulley assembly according to claim 6, characterised in that said annular unit (76) at least partially covers said spiral spring (66) in an axial direction as well.

9. The pulley assembly according to any of the preceding claims, characterised in that said control means (78) at least partially surround said elastic torsional assembly (54) .

10. The pulley assembly according to any of the preceding claims, characterised in that a crown (19; 61) of said pulley (4; 53) at least partially surrounds said control means (25; 78) in a radial direction.

11. The pulley assembly according to claim 10, characterised in that said control means (78) at least partially surround a band spring (28; 80) of said unidirectional coupling (13, 28, 19; 65, 79, 80) in a radial direction.

12. The pulley assembly according to any of the preceding claims, characterised in that said rolling bearing (21) is at least partially surrounded by said control means (25) .

13. The pulley assembly according to any of the preceding claims, characterised by comprising a dynamic torsional dampener (3, 52) connected to said hub (2; 51).

14. The pulley assembly according to any of the preceding claims, characterised in that said rolling bearing (21) and said elastic torsional assembly (5; 54) are side by side.

15. The pulley assembly according to any of the preceding claims, characterised in that said control means (78) comprise a coil cooperating with a armature (26; 79) and in that said coil (78) directly faces at least one portion of said armature (83) to maximise the attractive force produced by the electromagnetic field generated by said coil (78) .

16. A control method for an internal combustion engine comprising an endless drive to lock a pulley assembly according to any of the preceding claims, characterised by comprising the steps of:

- detecting the angular speed of a crankshaft of said engine;

- comparing said angular speed with a predetermined limit value; and

- closing said unidirectional coupling (13, 28, 19; 65, 79, 80) when said angular speed drops below said predetermined limit value if said unidirectional coupling (13, 28, 19; 65, 80) is open