Pulley decoupler

Abstract

The invention relates to a pulley decoupler (2) for transmitting torque between a belt (5) of a belt drive and a shaft (4) to which the belt is drivingly connected, comprising: - a hub (11) which is fastened to the shaft, - a pulley (10) which is rotatably mounted on the hub, and - a series circuit of a helical torsion spring (20), a winding band (19) and a transmission sleeve (24), the winding band surrounding the helical torsion spring with a radial gap, the transmission sleeve surrounding the winding band and transmitting torque between the winding band and the helical torsion spring, wherein the outer circumference of the winding band is in frictional contact with an inner lateral surface (22) which co-rotates with the pulley, and the outer circumference of the winding band is also in frictional contact with an inner lateral surface (23) of the transmission sleeve, and wherein the end of the helical torsion spring is in contact with a radially inwardly extending spring plate (27) of the transmission sleeve. The diameter of the inner lateral surface of the transmission sleeve and the radial gap between the winding band and the helical torsion spring should decrease towards the spring end (26) which is in contact with the spring plate of the transmission sleeve.

Description

TECHNICAL FIELD

[0001] The invention relates to a pulley decoupler for transmitting torque between a belt of a belt drive and a shaft in driving connection with the belt, the pulley decoupler comprising:

[0002] - a hub, which is fastened to the shaft,

[0003] - a pulley, which is mounted in a rotatable manner on the hub,

[0004] - and a series circuit of a helical torsion spring, a wrap-around band and a transmission sleeve, the series circuit being arranged in the torque flow between the pulley and the hub, the wrap-around band surrounding the helical torsion spring with a radial gap, the transmission sleeve surrounding the wrap-around band and transmitting torque between the wrap-around band and the helical torsion spring.

[0005] The outer periphery of the wrap-around band is in frictional contact with an inner lateral surface that co-rotates with the pulley, and the outer periphery of the wrap-around band is also in frictional contact with an inner lateral surface of the transmission sleeve, and the end of the helical torsion spring is in contact with a radially inwardly extending spring plate of the transmission sleeve. BACKGROUND

[0006] It is known that torsional vibrations and torsional irregularities introduced from the crankshaft of an internal combustion engine into a belt drive of an auxiliary unit can be compensated by a pulley decoupler, which is also referred to simply as a decoupler or isolator, and which is usually designed as a generator pulley. The wrap-around band serves as a one-way clutch, which transmits torque from the pulley to the hub when it is closed, wherein the elasticity of the helical torsion spring connected in series with the wrap-around band smoothes the torsional irregularities originating from the belt drive. When the pulley is delayed in rotation, the wrap-around band opens, wherein - and vice versa - no significant torque is transmitted from the hub to the pulley, so that an inert generator shaft can overtake the pulley.

[0007] A generic pulley decoupler is known, for example, from DE 10 2015 202 527 B3, DE 10 2015 224 608 A1, DE 10 2016 211 558 A1 or US 7,975,821 B1. The rotational speed of the pulley decoupler, which is usually three to four times higher than the rotational speed of the crankshaft, means that even small deviations in the coaxiality of the helical torsion spring to the rotational axis can produce disruptive imbalances in the rotating pulley decoupler.

[0008] As a solution to this problem, it is proposed in DE 10 2018 108 426 A1, which is also generic, to design the winding band end extending over the side of the transmission sleeve to have a radial notch deviating from the circular shape, so that the winding band end centers the spring end extending therein with a relatively small inner sleeve circle.

[0009] The invention is based on the object of improving the balancing of a pulley decoupler of the above-mentioned type. SUMMARY

[0010] The solution of the invention results from the features of claim 1. Thus, the diameter of the inner lateral surface of the transmission sleeve and the radial clearance between the winding band and the helical torsion spring should decrease with proximity to the spring end in contact with the spring plate of the transmission sleeve. The decrease in the radial clearance makes it possible to center the spring end extending over the side of the transmission sleeve about the axis of rotation of the pulley decoupler optimally by means of the inner periphery of the winding band. The radial notch at the end of the winding band mentioned above can be omitted, since the winding band is wound with a constant wire cross section and one of the following geometries:

[0011] - the winding band is completely cylindrical. The decrease in the inner diameter of the lateral surface of the transmission sleeve forces the winding of the winding band to adapt to the inner diameter of the lateral surface of the drive sleeve with a correspondingly reduced winding diameter.

[0012] - the winding band is completely cylindrical, except for one or several end turns with a reduced diameter. The decrease in the inner diameter of the lateral surface of the transmission sleeve forces the winding adjacent to the end winding to adapt to the inner diameter of the lateral surface of the transmission sleeve with a correspondingly reduced diameter. The reduction in the end winding diameter makes it easier for the winding band to fit into the transmission sleeve, wherein there is a relatively large overlap (pressure) between the two components.

[0013] - the winding diameter of the winding band decreases according to its inner diameter in the axial overlap area with the transmission sleeve. The assembly of the winding band in the transmission sleeve is quite simple.

[0014] The diameter of the inner lateral surface of the transmission sleeve can decrease in stages, but preferably continuously. In this case, the inner lateral surface of the transmission sleeve is particularly conical or parabolic in shape. BRIEF DESCRIPTION OF DRAWINGS

[0015] Further features of the invention emerge from the following description and the drawings, in which an exemplary embodiment of a pulley decoupler according to the invention for use with an electric generator arranged in a belt drive of an auxiliary unit of an internal combustion engine is shown. In the drawings:

[0016] Figure 1 A schematic view of a belt drive is shown;

[0017] Figure 2 The pulley decoupler is shown in longitudinal section;

[0018] Figure 3 The pulley decoupler is shown in an exploded perspective view from a first-person view.

[0019] Figure 4 The pulley decoupler is shown in an exploded perspective view from a second viewpoint. Detailed Implementation

[0020] Figure 1 The auxiliary unit of the pulley 1 of the internal combustion engine shown includes a pulley decoupler 2 according to the invention, which is arranged on the generator 3 and drives the generator shaft 4. The belt 5, circulating in the direction shown, is driven by the crankshaft pulley 6 and wound around the deflection pulley 7, the air conditioning compressor pulley 8, the belt tensioner pulley 9, and the pulley 10 of the pulley decoupler 2.

[0021] Figures 2 to 4 The pulley decoupling device 2 is shown in different representations. The pulley 10 is hollow cylindrical and has outwardly facing surfaces with multiple V-shaped profiles according to the belt 5. Figure 3 The pulley 10, driven by the belt 5 in the rotational direction shown, is rotatably mounted on a hub 11, which is securely screwed onto the shaft 4 of the generator 3. For this purpose, the hub 11 has an internal thread 12 in its central portion and a hexagonal notch 13 at its front end, serving as an engagement profile for a screwing tool. The pulley 10 is mounted radially and axially on the hub 11 at the generator end by means of rolling bearings, and radially on the hub at the end away from the generator by means of sliding bearings. The rolling bearings are single-row ball bearings 14 sealed on both sides, and the sliding bearings are radial bearing rings 15 made of polyamide, which axially enclose a circumferential groove 16 in the hub 11 and slide directly in contact with the inner lateral surface of the pulley 10. The pulley 10 has a stepped diameter expansion portion 17 at its end away from the generator, into which a protective cover 18 is inserted after the pulley decoupler 2 has been screwed onto the shaft 4.

[0022] The components necessary for the function of the belt pulley decoupler 2 are a one-way clutch designed to wind the belt 19 and a helical torsion spring 20 connected in series with the wound belt 19 with respect to the torque flow from the belt pulley 10 to the wheel hub 11 - this helical torsion spring ideally extends coaxially to the axis of rotation 21 of the belt pulley decoupler 2 in order to avoid unwanted imbalances. The wound belt 19 is arranged radially between the belt pulley 10 and the helical torsion spring 20 and encloses the helical torsion spring 20 with a radial gap. The helical torsion spring 20 is wound on the left side and has a trapezoidal wire cross section. The wound belt 19 is wound on the right side in a fully cylindrical manner and has a rectangular wire cross section that is constant over all windings.

[0023] The wound belt 19 and the helical torsion spring 20 have handleless ends on both sides, which radially widen the windings of the wound belt 19 or the helical torsion spring 20 during torque transmission. The outer periphery of the wound belt 19 is in frictional contact with an inner lateral surface 22 that rotates together with the belt pulley 10 on the one hand and with an inner lateral surface 23 of a transmission sleeve 24 that can rotate relative to the belt pulley 10 on the other hand and supports itself against the inner lateral surfaces 22, 23 while transmitting torque. The transmission sleeve 24 is connected in series with the wound belt 19 and the helical torsion spring 20 in the torque flow and transmits torque from the wound belt 19 to the helical torsion spring 20. The inner lateral surface 22 is formed by a drive sleeve 25 that is pressed into the belt pulley 10, which, as is explained further below, radially supports the transmission sleeve 24 and, like the transmission sleeve 24, is heat treated for the purpose of its surface wear resistance. However, the belt pulley 10 is not hardened.

[0024] The wound belt 19 enables the shaft 4 of the generator 3 and the wheel hub 11 fastened to it to be overrun relative to the belt pulley 10. In this overrun operation of the belt pulley decoupler 2, the wound belt 19 slips in the transmission sleeve 24 and / or the drive sleeve 25 and the torque that can be transmitted is limited to the sliding friction torque between the two pairs of sliding contacts.

[0025] The drive-side spring end 26 of the helical torsion spring 20 bears against a spring plate 27, which is part of the transmission sleeve 24 and extends radially inward from the inner lateral surface 23 of the transmission sleeve. The spring end 28 on the output side rests against a spring plate 29, which cannot rotate with the wheel hub 11 and is designed in one piece with the wheel hub 11 in the present case. The helical torsion spring 20 is tensioned with an axial pretension between the spring plates 27, 29. The two spring plates 27, 29 each have a spring contact surface that springs back at a peripheral step 30 or 31, respectively. The torque transmitted from the belt pulley 10 to the wheel hub 11 is transmitted via the pressure contact of the peripheral faces of the spring ends 26, 28 with the step 30, 31 of the spring plates 27, 29, respectively.

[0026] To avoid spring unbalance, the ideal coaxial centering of the helical torsion spring 20 about the rotation axis 21 is achieved on the output-side spring end 28 by a spring plate 29 which surrounds the spring end 28 with a narrow radial gap. The drive-side spring end 26, which rests against the spring plate 27 of the drive sleeve 24, is centered by a likewise narrow radial gap between the winding strap 19 and the helical torsion spring 20. Starting from the drive sleeve 25, this radial gap decreases towards the spring end 26, in order to leave sufficient free space for the radial expansion of the spring-loaded coil between the spring ends 26, 28 during torque transmission. The decrease in the radial gap is produced by a conical decrease in the inner diameter of the drive sleeve 24, which in this case decreases by approximately 0.3 mm, which forces the winding diameter of the winding strap 19, which is supported in the drive sleeve 24 in an oversized dimension, to decrease correspondingly.

[0027] As an alternative to the completely cylindrical shape of the winding strap in the present case, its ends can be wound with a reduced winding diameter in order to make it easier to thread the winding strap into the drive sleeve 24.

[0028] The rotational mounting of the drive sleeve 24 takes place radially via the drive sleeve 25 on the one hand and radially and axially via a sliding bearing ring 32 made of polyamide, which is inserted between the drive sleeve 24 and the ball bearing 14, on the other hand. The radial bearing formed by the drive sleeve 25 is a diameter step 33, which is formed on the end portion of the drive sleeve 25 facing the drive sleeve 24 and whose outer lateral surface radially bears against the inner lateral surface of a diameter step 34 on the drive sleeve 24. The sliding bearing ring 32 encloses the drive sleeve 24 on the outer lateral surface of a diameter step 35 in order to radially bear the drive sleeve 24 against the inner lateral surface 36 of the pulley 10. The sliding bearing ring 32 axially bears the drive sleeve 24, which can be acted upon by the pretensioning force of the helical torsion spring 20, against the outer ring of the ball bearing 14.

[0029] The present rotational bearing makes it possible to mount the drive sleeve 24 on the one hand without contact with the inner lateral surface 36 of the non-hardened pulley 10 and on the other hand to dimension the sleeve wall thickness to be approximately the same size and stable as the wall thickness of the drive sleeve 25.

[0030] In contrast to the possible alternative axial bearing of the drive sleeve 24 against the inner ring of the ball bearing 14 and its radial bearing against the wheel hub 11, the relative movement on the sliding bearing ring 32 only occurs when the pulley decoupler 2 is overdimensioned. Since the time portion of the overdimensioning operation is significantly smaller than the normal operation (transmission of torque), this bearing design contributes to reducing the frictional losses in the operation of the pulley decoupler 2.

Claims

1. A pulley decoupling device (2) for transmitting torque between a belt (5) of a belt drive and a shaft (4) driven by said belt, said pulley decoupling device comprising: - Hub (11), the hub being fastened to the shaft (4), -Pulley (10), which is rotatably mounted on the hub (11), - and a series circuit of a helical torsion spring (20), a winding belt (19), and a transmission sleeve (24), the series circuit being arranged in the torque flow between the pulley (10) and the hub (11), the winding belt surrounding the helical torsion spring (20) with radial clearance, and the transmission sleeve surrounding the winding belt (19) and transmitting the torque between the winding belt (19) and the helical torsion spring (20). The outer periphery of the winding tape (19) is in frictional contact with the inner lateral surface (22) that rotates together with the pulley (10), and the outer periphery of the winding tape is also in frictional contact with the inner lateral surface (23) of the transmission sleeve (24), and the end of the helical torsion spring (20) is in contact with the radially inwardly extending spring plate (27) of the transmission sleeve (24). The characteristic feature is that the diameter of the inner lateral surface of the transmission sleeve (24) and the radial gap between the winding tape (19) and the helical torsion spring (20) should decrease as the spring end (26) approaches the spring plate (27) of the transmission sleeve (24).

2. The pulley decoupling device (2) according to claim 1, characterized in that, The diameter of the inner side surface of the transmission sleeve (24) decreases continuously.

3. The pulley decoupling device (2) according to claim 2, characterized in that, The inner lateral surface (23) of the transmission sleeve (24) is conical or parabolic.

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