Double belt tensioner, belt drive and motor vehicle

Abstract

Double belt tensioner (1) for tensioning a belt (2) of a belt drive (3) of a belt starter generator for a motor vehicle, comprising a holding device (4) with a recess (5) for arranging the double belt tensioner (1) on a first pulley (6) of the belt drive (3), a first tensioning roller (7) with a first axis of rotation (8) and a second tensioning roller (9) with a second axis of rotation (10) for tensioning the belt (2), and a tensioning device (11) for generating a tensioning force between the first tensioning roller (7) and the second tensioning roller (9), wherein the first tensioning roller (7) and the second tensioning roller (9) are rotatably arranged on the holding device (4) about a common pivot axis (12), wherein the first tensioning roller (7) and the second tensioning roller (9) are movably arranged relative to each other on the holding device (4), and wherein the tensioning device (11) is designedby moving the first tensioning roller (7) and the second tensioning roller (9) relative to each other to increase the tensioning force between the first tensioning roller (7) and the second tensioning roller (9), characterized in that the first tensioning roller (7) has a first tensioning roller diameter (13) and the second tensioning roller (9) has a second tensioning roller diameter (14), wherein the first tensioning roller diameter (13) is larger than the second tensioning roller diameter (14), and wherein the first tensioning roller diameter (13) is between 120% and 160% of the second tensioning roller diameter (14).

Description

[0001] The invention relates to a double belt tensioner for tensioning a belt of a belt drive of a belt-driven starter generator of a motor vehicle. The invention further relates to a belt drive of a belt-driven starter generator of a motor vehicle with a double belt tensioner according to the invention, and to a motor vehicle with a belt-driven starter generator according to the invention.

[0002] Common belt drives, for example, feature a drive pulley and a driven pulley, on which a belt, such as a V-belt or toothed belt, is mounted for power transmission. To transmit torque from the drive pulley to the driven pulley, belts are typically pre-tensioned. This prevents or at least reduces slippage between the belt and the drive or driven pulley. This is particularly important in belt drives where torque transmission occurs through friction rather than positive engagement.

[0003] Free sections of the belt – that is, sections of the belt that are not in contact with the drive pulley, the driven pulley, idler pulleys, or tensioning rollers – are called runs. When torque is transmitted from the drive pulley to the belt, different runs are subjected to different loads. A run subjected to tensile stress during operation, which is located directly in front of the drive pulley with respect to the direction of rotation, is called the load run or pulling run. A run subjected to compressive stress during operation is called the slack run or pulled run. The slack run is therefore located directly behind the drive pulley with respect to the direction of rotation.

[0004] The belt has a first wrap section, which engages the drive pulley at a first wrap angle, and a second wrap section, which engages the driven pulley at a second wrap angle. The larger the wrap angle, the higher the transmissible torque. Another essential factor for torque transmission is the belt tension. While the belt always has a higher tension than the pre-tension on the loaded side during operation, it can have a lower tension than the pre-tension on the slack side. Therefore, the maximum transmissible torque of the belt drive is limited.

[0005] To prevent such a reduction in belt tension and the associated reduction in transmissible torque, many belt drives have a tensioning device on the slack side of the belt. This device tensions the belt and thus ensures a minimum wrap angle at the drive pulley and / or the driven pulley. Such tensioning devices, for example, have a tensioning roller that can be pressed against the belt by means of a spring element, tensioning the belt on the slack side and thus ensuring at least a minimum belt tension for the belt drive.

[0006] Furthermore, special belt drives are known in which a static division into drive and driven pulleys is not possible, as these special belt drives have different operating modes. In one operating mode, a first pulley serves as the drive pulley and a second pulley as the driven pulley, while in a second operating mode, the first pulley serves as the driven pulley and the second pulley as the drive pulley. This is the case, for example, with belt drives on electric machines, which can be operated as an electric motor in the first operating mode and as a generator in the second. An example of such an electric machine is a belt-driven starter generator. Switching between the operating modes can, for example, reverse the direction of the load and slack sides.In belt drives with a static division of drive pulley and driven pulley, which can be operated with alternating directions of rotation, a reversal of the load side and slack side also takes place when the direction of rotation is changed.

[0007] Because of the reversal of the load and slack sides, such belt drives often feature double belt tensioners, which have a tensioning roller in both the load and slack sides. This ensures tension in the slack side in every operating mode of the belt drive. Known double belt tensioners have two tensioning rollers arranged on a mounting bracket, one of which can be positioned in the load side and the other in the slack side. The tensioning rollers are coupled to each other via a tensioning device and can thus be pressed against the belt. This ensures improved belt tension in the slack side.

[0008] Due to the coupling of the tensioning pulleys by the tension spring, a force equilibrium exists at the tensioning pulleys in every operating state, resulting from the forces within the belt strand and the wrap angle of the tensioning pulleys. At rest, all forces within the belt strand are equal and correspond to a pretension force on the belt. Because of this force equilibrium, the wrap angles of the tensioning pulleys are also equal.

[0009] The function of the tensioning pulley is to tension the belt on the slack side. In double belt tensioners, one tensioning pulley is always positioned on the slack side to tension the belt. The other tensioning pulley supports the double belt tensioner on the loaded side. This achieves an operating-condition-dependent tension on the slack side.

[0010] Various belt tensioners are known from the documents DE 10 2011 084 680 B3, EP 0 911 540 A2 and WO 2013 142 951 A1.

[0011] Common double belt tensioners have the disadvantage that, under high load on the belt drive or the belt itself, the belt in the load-bearing section can become so tensioned that it reaches a wrap angle of 0° at the first tensioning pulley and even lifts off it. When the belt lifts off the tensioning pulley, a dynamic force increase occurs in the belt, which is detrimental to the operation of the belt drive. Furthermore, undesirable noise can occur when the belt re-seats itself onto the tensioning pulley.

[0012] It is therefore an object of the present invention to provide a double belt tensioner for tensioning a belt of a belt drive of a belt-driven starter generator for a motor vehicle, as well as a belt drive of a belt-driven starter generator for a motor vehicle and a motor vehicle with a belt drive, which eliminate or can at least partially eliminate these disadvantages. In particular, it is an object of the present invention to provide a double belt tensioner for a belt drive, as well as a belt drive with a double belt tensioner and a motor vehicle with a belt drive, in which, with simple and reliable means, the lifting of the belt from the tensioning pulleys of the double belt tensioner is reduced, the wrap angle of the belt on the tensioning pulleys is increased under high belt loads, and the provision of a minimum belt tensioning force is improved.

[0013] The aforementioned problem is solved by the claims. Accordingly, the problem is solved by a double belt tensioner for a belt drive according to the features of claim 1, a belt drive with a double belt tensioner according to the features of claim 8, and a motor vehicle with a belt drive according to the features of claim 9. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawings. Features and details described in connection with the double belt tensioner according to the invention naturally also apply in connection with the belt drive and the motor vehicle according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always makes, or can make, reciprocal references.

[0014] According to a first aspect of the invention, the problem is solved by a double belt tensioner for tensioning a belt of a belt drive of a belt-driven starter generator for a motor vehicle. The double belt tensioner has a holding device with a recess for mounting the double belt tensioner on a first pulley of the belt drive. Furthermore, the double belt tensioner has a first tensioning roller with a first axis of rotation and a second tensioning roller with a second axis of rotation for tensioning the belt, as well as a tensioning device for generating a tensioning force between the first tensioning roller and the second tensioning roller. The first tensioning roller and the second tensioning roller are rotatably mounted on the holding device about a common pivot axis, wherein the first tensioning roller and the second tensioning roller are movable relative to each other on the holding device.The clamping device is designed to increase the clamping force between the first and second clamping rollers by moving them relative to each other. The first clamping roller has a first clamping roller diameter, and the second clamping roller has a second clamping roller diameter, the first clamping roller diameter being larger than the second clamping roller diameter. The first clamping roller diameter is between 120% and 160% of the second clamping roller diameter.

[0015] The holding device is designed to hold the first and second tensioning rollers. It allows the first and second tensioning rollers to move about a common pivot axis. Preferably, this common pivot axis coincides with, or is at least adjacent to, a pulley axis. The common pivot axis and the pulley axis run parallel or at least substantially parallel to each other.

[0016] The holding device has a recess through which a first pulley of a belt drive, or at least an axle of the first pulley, can pass. Thus, the double belt tensioner can be arranged on the first pulley in such a way that the first pulley is freely rotatable. The recess is preferably round or substantially round. The first pulley is, for example, coupled to or held on an output or input shaft of a belt-driven starter generator of a motor vehicle. Preferably, the double belt tensioner can be arranged on the first pulley with the recess coaxial to the first pulley. A coaxial arrangement of the double belt tensioner on the first pulley means that the axis of rotation of the first pulley is arranged coaxially with a central axis of the recess.The holding device preferably has at least one fastening device, in particular a bore, for fastening the holding device to the belt starter generator, in particular to a stationary part of the belt starter generator, in particular the housing of the belt starter generator.

[0017] The first tensioning pulley is rotatably mounted on the holding device about the first axis of rotation, and the second tensioning pulley is rotatably mounted about the second axis of rotation. This allows the first and second tensioning pulleys to roll along the belt. Furthermore, the first and second tensioning pulleys are arranged on the holding device so that they can move relative to each other. Thus, the first and second tensioning pulleys can be moved, for example, towards or away from each other. The holding device is preferably designed to allow such relative movement along a curved path around the common pivot axis, in particular a circular path with the common pivot axis as the center of the circle.

[0018] The tensioning device is designed to provide a tension force by which the first and second tensioning rollers can be moved towards each other. Furthermore, the tensioning device is designed to increase the tension force by moving the first and second tensioning rollers away from each other, preferably proportionally to the distance between them. Depending on the operating condition, the belt can be tensioned in the slack side by means of either the first or second tensioning roller, with the double belt tensioner being supported against the belt in the loaded side by means of the other second or first tensioning roller located in the loaded side.The clamping device is preferably arranged or attached to a bearing or holder for the first clamping roller and a bearing or holder for the second clamping roller, such that the first clamping roller is rotatable about the first axis of rotation and the second clamping roller is rotatable about the second axis of rotation relative to the clamping device. Preferably, the clamping device is designed in the shape of an annular segment or substantially in the shape of an annular segment. It is further preferably that a central point of the annular clamping device is arranged on the common axis of rotation. It is also preferably that the clamping device is made of spring steel or consists at least substantially of spring steel.

[0019] The first tensioner pulley has a larger diameter than the second, resulting in an asymmetrical design for the double belt tensioner. This asymmetry offers the advantage of ensuring a larger belt wrap angle on the tensioner pulleys compared to similar double belt tensioners with equally sized pulleys. This prevents the belt from lifting off the tensioner pulleys, even under higher loads on the loaded side, using simple and cost-effective methods. This is particularly advantageous for belt drives with alternating loaded and unloaded sides. Another benefit of differently sized tensioner pulleys is that the double belt tensioner can be optimally adapted to a given installation space, especially one with an asymmetrical design, by positioning the first tensioner pulley in a relatively large area and the second in a relatively small area.The diameter of the first tensioner pulley is between 120% and 160% of the diameter of the second tensioner pulley. With this ratio of tensioner pulley diameters, an improved wrap angle between the first and second tensioner pulleys can be achieved.

[0020] In a preferred embodiment of the invention, the first and second tensioning pulleys of a double belt tensioner are arranged on the holding device so as to be movable relative to each other about a common pivot axis. Thus, the tensioning force of the double belt tensioner can be increased by moving the first and second tensioning pulleys away from each other along a cam track. This allows for a more compact design of the double belt tensioner and improved belt tension under changing operating or load conditions of the belt starter generator, particularly under relatively high forces in the load-bearing section.

[0021] Preferably, in a double belt tensioner, the distance between the first axis of rotation of the first tensioning pulley and the common pivot axis corresponds to the distance between the second axis of rotation of the second tensioning pulley and the common pivot axis. This allows for a more compact design of the double belt tensioner and achieves better belt tension under changing operating or load conditions of the belt starter generator, especially under relatively high forces in the load-bearing section. The installation space required for the double belt tensioner can thus be reduced.

[0022] According to the invention, a double belt tensioner can be provided with a holding device comprising a first holding section and a second holding section, wherein the first holding section and the second holding section are rotatable relative to each other about the common pivot axis. The first tensioning roller is arranged on the first holding section and the second tensioning roller on the second holding section. Such a holding device preferably has a third holding section that can be attached to the belt starter generator. The first holding section and the second holding section are movable relative to each other and to the third holding section and are preferably guided along a path on the third holding section, in particular on a rail. This path is preferably a partial circle with the common pivot axis as its center point. Such a holding device has a compact design and requires relatively little installation space.The tensioning device is preferably attached to both the first and second retaining sections, so that the first retaining section is directly coupled to the second retaining section via the tensioning device. Such a double belt tensioner is easy to install and has a robust and compact design.

[0023] In a double belt tensioner, it is preferred that the first tensioning roller is movably held relative to the first holding section along a first track, and / or that the second tensioning roller is movably held relative to the second holding section along a second track. For this purpose, the first holding section preferably has a first guide section for guiding the first tensioning roller along the first track, and the second holding section preferably has a second guide section for guiding the second tensioning roller along the second track. The first guide section and the second guide section each preferably have a guide rail and / or a guide groove. Preferably, the first track and the second track each run linearly. A preferred orientation of the first track and the second track is in the direction of the common pivot axis.This has the advantage that, with a double belt tensioner according to the invention, additional adjustment of the first and second tensioning pulleys is possible. Thus, for example, the tensioning force or tension of the belt can be changed. This can be advantageous, for instance, if the belt stretches. Furthermore, this improves the running characteristics of the belt drive, particularly when switching operating states or when changing between the loaded and unloaded sides. Another advantage is that the lever arms of the first and second tensioning pulleys are variable and can therefore be adjusted as needed.

[0024] Preferably, in a double belt tensioner, the first retaining section has a first spring element for holding the first tensioning pulley in a first relative position to the first retaining section, and / or the second retaining section has a second spring element for holding the second tensioning pulley in a second relative position to the second retaining section. The first and second spring elements are preferably designed as coil springs or disc springs. Such spring elements have the advantage that the tensioning force or belt tension can be improved.

[0025] Preferably, in a double belt tensioner, the diameter of the first tensioner pulley is between 135% and 145% of the diameter of the second tensioner pulley. For example, the diameter of the first tensioner pulley is 70 mm, and the diameter of the second tensioner pulley is 50 mm. With such a ratio of tensioner pulley diameters, an improved wrap angle between the first and second tensioner pulleys can be achieved.

[0026] Furthermore, according to the invention, a double belt tensioner can be provided in such a way that the first holding section has a first adjusting element for adjusting the first relative position of the first tensioning pulley to the first holding section, and / or that the second holding section has a second adjusting element for adjusting the second relative position of the second tensioning pulley to the second holding section. This has the advantage that improved adjustment of the first and second tensioning pulleys can be achieved.

[0027] According to a second aspect of the invention, the problem is solved by a belt drive for a belt-driven starter generator for a motor vehicle. The belt drive comprises a first pulley, at least one second pulley, a belt guided around the first pulley and the at least one second pulley, and a double belt tensioner according to the first aspect of the invention for tensioning the belt. The belt drive according to the invention is preferably designed such that the belt-driven starter generator can be used both as a motor and as a generator. The double belt tensioner is therefore arranged on the belt drive such that the double belt tensioner tensions a slack side of the belt drive both when the belt-driven starter generator is operating as a motor and when it is operating as a generator.The belt drive according to the second aspect of the invention has the same advantages as the double belt tensioner according to the first aspect of the invention.

[0028] According to a third aspect of the invention, the problem is solved by a motor vehicle with a belt-driven starter generator comprising a belt drive according to the invention. The belt drive according to the invention includes a double belt tensioner according to the second aspect of the invention. The motor vehicle according to the third aspect of the invention thus has the same advantages as the belt drive according to the second aspect of the invention.

[0029] The double belt tensioner according to the invention for tensioning a belt of a belt drive of a belt-driven starter generator for a motor vehicle, as well as a belt drive of a belt-driven starter generator for a motor vehicle according to the invention, are explained in more detail below with reference to the drawings. The drawings schematically show: Fig. 1 in a perspective view a preferred first embodiment of a double belt tensioner according to the invention; Fig. 2 in a perspective view a preferred second embodiment of a double belt tensioner according to the invention; Fig. 3 in a side view a preferred embodiment of a belt drive according to the invention for a belt starter generator for a motor vehicle; and Fig. 4 in a top view a motor vehicle with a belt drive according to the invention.

[0030] In Fig. Figure 1 is a preferred first embodiment of a double belt tensioner 1 according to the invention, shown schematically in a perspective view. The double belt tensioner 1 has a holding device 4 with a first holding section 15, a second holding section 16, and a third holding section 24. The first holding section 15 and the second holding section 16 are rotatably guided about a common pivot axis 12 on the third holding section 24. A first tensioning roller 7 with a first tensioning roller diameter 13 is rotatably arranged about a first axis of rotation 8 on the first holding section 15. A second tensioning roller 9 with a second tensioning roller diameter 14 is rotatably arranged about a second axis of rotation 10 on the second holding section 16.

[0031] The third retaining section 24 has a recess 5 for the passage of an axle of a first pulley 6 (not shown) of a belt-driven starter generator (not shown). In this first embodiment, the recess 5 has a round cross-section and is arranged coaxially with the common pivot axis 12. According to the invention, the cross-section of the recess 5 can also have a shape other than round. The first tensioning pulley 7 and the second tensioning pulley 9 are coupled to each other via a tensioning device 11. The tensioning device 11 is designed to generate a tensioning force when the first tensioning pulley 7 and the second tensioning pulley 9 are moved apart, by means of which the first tensioning pulley 7 and the second tensioning pulley 9 can be moved towards each other. The third retaining section 24 has three mounting holes 23 for attaching the double belt tensioner 1 to the belt-driven starter generator, for example by means of corresponding mounting bolts.

[0032] In Fig. Figure 2 shows a preferred second embodiment of a double belt tensioner 1 according to the invention, schematically depicted in a perspective view. The double belt tensioner 1 essentially corresponds to the double belt tensioner 1 from [reference missing]. Fig. 1 and differs in a first guide device (hidden in this illustration) for guiding the first tension roller 7 on a first track 17 relative to the first retaining section 15, and a second guide device (hidden in this illustration) for guiding the second tension roller 9 on a second track 18 relative to the second retaining section 16. A first spring element 19 is arranged on the first retaining section 15 for holding the first tension roller 7 in a first relative position to the first retaining section 15. A second spring element 20 is arranged on the second retaining section 16 for holding the second tension roller 9 in a second relative position to the second retaining section 16. This means that by moving the first tension roller 7 from the first relative position along the first track 17, a restoring force towards the first relative position can be generated in the first spring element 19.Furthermore, by moving the second tension roller 9 from the second relative position along the second track 19, a restoring force towards the second relative position can be generated in the second spring element 20.

[0033] Fig. Figure 3 schematically shows a preferred embodiment of a belt drive 3 according to the invention for a belt-driven starter generator for a motor vehicle in a side view. The belt drive 3 has a first pulley 6, a second pulley 21, and a third pulley 22, which are connected or coupled to each other via a belt 2. A torque from the first pulley 6 can be transmitted via the belt 2 to the second pulley 21 and the third pulley 22, and vice versa. The first pulley 6 is, for example, directly coupled to the belt-driven starter generator or designed as part of the belt-driven starter generator. The second pulley 21 is, for example, directly coupled to a crankshaft, and the third pulley 22 is coupled to another unit.This additional unit could be, for example, a compressor, in particular an air conditioning compressor, a water or power steering pump, a charger, or the like.

[0034] A double belt tensioner 1 according to the invention is arranged on the first pulley 6 for tensioning the belt 2. The double belt tensioner 1 has a first tensioning roller 7 rotatable about a first axis of rotation 8 and a second tensioning roller 9 rotatable about a second axis of rotation 10, the first tensioning roller 7 having a larger diameter than the second tensioning roller 9. The first tensioning roller 7 and the second tensioning roller 9 are coupled to each other via a tensioning device 11 for tensioning the belt 2. The first tensioning roller 7, together with the second tensioning roller 9 and the tensioning device 11, can be pivoted about a common pivot axis 12, which runs coaxially with the first pulley 6. Such pivoting depends on the operating and load conditions of the belt drive 3. The space requirement of the double belt tensioner 1 can be derived from the maximum pivoting range of the first tensioning roller 7 and the second tensioning roller 9.Given a limited installation space, the first tensioning roller 7 and the second tensioning roller 9 are preferably arranged such that the available installation space is optimally utilized over the entire pivoting range. By means of the belt drive 3 according to the invention, tension of the belt 2 in the slack side is ensured in every operating state of the belt starter generator or the belt drive 3.

[0035] Fig. Figure 4 schematically shows a top view of a motor vehicle 25 with a belt drive 3 according to the invention. Reference symbol list 1 double belt tensioner 2 belts 3 Belt drive 4 Holding device 5 Exclusion 6 first pulley 7 first tension roller 8 first axis of rotation 9 second tension roller 10 second axis of rotation 11 Clamping device 12 common pivot axis 13 first tension roller diameter 14 second tension roller diameter 15 first stopping section 16 second stopping section 17 first lane 18 second lane 19 first spring element 20 second spring element 21 second pulley 22 third pulley 23 Mounting holes 24 third stopping section 25 motor vehicle

Claims

[1] Double belt tensioner (1) for tensioning a belt (2) of a belt drive (3) of a belt starter generator for a motor vehicle, comprising a holding device (4) with a recess (5) for arranging the double belt tensioner (1) on a first pulley (6) of the belt drive (3), a first tensioning roller (7) with a first axis of rotation (8) and a second tensioning roller (9) with a second axis of rotation (10) for tensioning the belt (2), and a tensioning device (11) for generating a tensioning force between the first tensioning roller (7) and the second tensioning roller (9), wherein the first tensioning roller (7) and the second tensioning roller (9) are rotatably arranged on the holding device (4) about a common pivot axis (12), wherein the first tensioning roller (7) and the second tensioning roller (9) are movably arranged relative to each other on the holding device (4), and wherein the tensioning device (11) is designedto increase the tension force between the first tension roller (7) and the second tension roller (9) by moving them relatively away from each other, characterized by , that the first tension roller (7) has a first tension roller diameter (13) and the second tension roller (9) has a second tension roller diameter (14), wherein the first tension roller diameter (13) is larger than the second tension roller diameter (14), wherein the first tension roller diameter (13) is between 120% and 160% of the second tension roller diameter (14). [2] Double belt tensioner (1) according to claim 1, characterized by , that the first tension roller (7) and the second tension roller (9) are arranged on the holding device (4) so ​​as to be movable relative to each other about the common pivot axis (12). [3] Double belt tensioner (1) according to claim 1 or 2, characterized by, that a distance of the first axis of rotation (8) from the common pivot axis (12) corresponds to a distance of the second axis of rotation (10) from the common pivot axis (12). [4] Double belt tensioner (1) according to one of the preceding claims, characterized by , that the holding device (4) has a first holding section (15) and a second holding section (16), wherein the first holding section (15) and the second holding section (16) are rotatable relative to each other about the common pivot axis (12), and wherein the first tension roller (7) is arranged on the first holding section (15) and the second tension roller (9) is arranged on the second holding section (16). [5] Double belt tensioner (1) according to claim 4, characterized by, that the first tension roller (7) is held movably on the first holding section (15) along a first track (17) and / or the second tension roller (9) is held movably on the second holding section (16) along a second track (18). [6] Double belt tensioner (1) according to claim 5, characterized by , that the first holding section (15) has a first spring element (19) for holding the first tension roller (7) in a first relative position to the first holding section (15) and / or that the second holding section (16) has a second spring element (20) for holding the second tension roller (9) in a second relative position to the second holding section (16). [7] Double belt tensioner (1) according to one of the preceding claims, characterized by , that the first tension roller diameter (13) is between 135% and 145% of the second tension roller diameter (14). [8] Belt drive (3) of a belt starter generator for a motor vehicle, comprising a first pulley (6), at least one second pulley (21), a belt (2) guided around the first pulley (6) and the at least one second pulley (21) and a double belt tensioner (1) for tensioning the belt (2), characterized by , that the double belt tensioner (1) is designed according to one of claims 1 to 7. [9] Motor vehicle (25) with a belt-driven starter generator (3) having a belt drive, characterized by , that the belt drive (3) is designed according to claim 8.

Images