Belt drive

Abstract

Belt drive (1) with a loop-shaped belt (6) which runs around a first pulley (2) and a second pulley (10), wherein the first pulley (2) and the second pulley (10) are rotatably mounted about parallel wheel axes (4, 14), wherein the belt (6) engages with its inner circumference on outer circumferential contours (5, 9) of the pulleys (2, 10) to transmit a torque between the pulleys (2, 10), wherein the belt (6) is a toothed belt (16) and the pulleys (2, 10) comprise gears (7, 11) which mesh the toothed belt (16), wherein in both regions of the belt (6) between the pulleys (2, 10) a tensioning roller (17) bears against an outer circumference of the belt (6), wherein the two tensioning rollers (17) are rotatably mounted about roller axes (19) which are parallel to the wheel axes (4, 14) run, with the two tension rollers (17) bearing against both belt pulleys (2, 10) under intermediate arrangement of the belt (6),wherein both tension rollers (17) have the same diameter, wherein a diameter of the outer circumferential contour (9) of the second pulley (10) is at least twice as large as a diameter of the outer circumferential contour (5) of the first pulley (2), wherein a wrap angle (20) of a wrap of the second pulley (10) with the belt (6) is greater than 270°, wherein the two tension rollers (17) are mounted in stationary rotary bearings (18), wherein the roller axes of the two tension rollers (17) have a fixed distance from each other, and wherein the two tension rollers (17) support the second pulley (10) in the direction towards the first pulley (2), characterized in that a wrap angle (21) of a wrap of the first pulley (2) with the belt (6) is greater than 200° and that the two tension rollers (17) support the first pulley (2) in the direction towards the second pulley (10). supported so that the belt (6) does not form a loose end.

Description

TECHNICAL AREA OF INVENTION

[0001] The invention relates to a belt drive with a loop-shaped belt that runs around a first belt pulley and a second belt pulley to transmit a torque between the belt pulleys.

[0002] The belt in question is a timing belt. STATE OF THE ART

[0003] DE 10 2011 006 890 A1 discloses a steering device for adjusting the steering angle of a wheel of a motor vehicle. A wheel carrier of the wheel is adjustable by means of a drive unit comprising a belt drive. One pulley is fixed on a drive shaft and another pulley of the belt drive is fixed on an output shaft. A belt running around the pulleys is supported at specific points between the pulleys on both sides of the distance between the wheel axles by one of the tensioning rollers. The roller axles of the tensioning rollers are at a fixed distance from each other. The tensioning rollers are mounted on a slide that is movable against a spring force transversely to the direction of the distance between the wheel axles. This necessarily results in a pronounced reversal of the known belt drive.

[0004] Tensioning pulleys are also used in other well-known belt drives. These tensioning pulleys serve not only to tension the belt but also to increase the area wrapped around the pulleys of the respective belt drive by the belt.

[0005] From DE 86 29 356 U1 and WO 88 / 03 620 A1, both from the same patent family, a device for backlash-free transmission and, if necessary, conversion of rotary motion is known using an endless transmission element designed as a loop and equipped with teeth. The endless transmission element is in constant engagement with a drive and a driven side. The loop of the endless transmission element wraps around two deflection rollers with its rear side. A gear on each side, one on the drive side and one on the driven side, engages with the teeth of the endless transmission element. This creates a larger area for the engagement of the gears on the drive and driven sides than if they were directly meshing with each other. The two gears engaging with the teeth of the endless transmission element can have different radii of curvature.The transmission element can also have teeth on both sides. In this case, the deflection rollers also have teeth on their circumference. The deflection rollers can also have different diameters to derive different rotational speeds from a common main shaft. In the known device, the drive and input gears, which engage with the teeth on the back of the loop-shaped transmission element, are driven against each other and away from the deflection rollers by the tension of the loop-shaped transmission element.

[0006] From JP H08-152 050 A, a device is known with a small drive gear and a large output gear around which a loop-shaped toothed belt runs. Between the two gears and at a distance from their outer circumferences, a pair of tensioning rollers engages the outer circumference of the toothed belt. These tensioning rollers increase the wrap angle, particularly on the small drive gear. The tension of the toothed belt exerts a force on the drive gear and the output gear towards each other. This force is not supported by the tensioning rollers.

[0007] From DE 17 75 648 A, a device for the combined support and drive of a rotating component, such as a hollow rotor of a debarking machine, is known. The rotating component is provided externally with one or more annular grooves for interaction with one or more drive belts or chains and is supported externally by or mounted on rollers. The rollers are also provided with annular grooves and are arranged around the annular grooves of the rotating component such that their annular grooves interact with the outer part of the drive belt(s) and support the rotating component, forming a bearing to absorb both radial and axial loads. The drive belt(s) are driven by a drive wheel located inside the drive belt(s). One of the rollers supporting the hollow rotor serves as a tensioning roller for the drive belt(s).

[0008] From US Patent 3,606,795 A, a mechanical motion device is known that has at least three cylindrical rollers with parallel cylindrical axes and at least two endless flexible belts. The belts are under tension and engage different areas of the rollers' circumferential surfaces, holding the rollers together. In one embodiment of the known device with four rollers, each belt encircles two rollers and runs between the other two rollers, with these other two rollers bearing against the outer circumference of the belt and, via the belt, against the encircled rollers. The cylindrical axes of the rollers are supported against each other solely by the belts circulating around the rollers.

[0009] From EP 0 599 312 A1, a belt drive for a gate drive is known. The belt drive comprises a flat or round belt guided over two rotating deflection elements, where at least one deflection element is driven and carries the belt. The driven deflection element is designed as a gear. A second gear is provided, which meshes loosely with the first gear and partially presses the belt into its tooth gaps. The driven gear can also mesh with two gears whose teeth engage slightly in the tooth gaps of the driven gear, deflecting the flat or round belt in such a way that it almost completely encircles the driven gear. The belt runs freely between the driven gear and a driven gear.

[0010] A belt drive with the features of the preamble of independent claim 1 is known from GB 2 361 886 A. The wrap angle of the belt around the smaller first of the two pulleys is approximately 180°. Between the pulleys, the belt runs around the tensioning rollers. Over short distances, however, the belt is neither guided by friction against the tensioning rollers nor does it engage with the pulleys.

[0011] To implement reduction gears in precision engineering without large reversing distances, strain wave gears are used, also known as wave gears, sliding wedge gears, or, by their English name, strain wave gears (SWG). In strain wave gears, an elastic transmission element is used, which is deformed by an eccentric element to engage with a rigid transition element in a local engagement area. This local engagement area is moved by rotating the eccentric element around an axis of rotation, dynamically deforming the elastic transmission element around the axis of rotation. Due to the different circumferences or tooth counts of the elastic transmission element and the rigid transmission element, the rigid transmission element is driven around the axis of rotation, while the elastic transmission element is only deformed and does not undergo any rotational movement.The rotational movement of the rigid transmission element is significantly reduced compared to the rotational movement of the eccentric element. Such tension wave drives are complex to manufacture and correspondingly expensive. TASK OF INVENTION

[0012] The invention is based on the objective of demonstrating a belt drive that is suitable for realizing reduction ratios in the field of precision mechanics without noticeable reversal. SOLUTION

[0013] The object of the invention is achieved by a belt drive with the features of independent claim 1. Preferred embodiments of the belt drive according to the invention are defined in the dependent claims. DESCRIPTION OF THE INVENTION

[0014] In a belt drive according to the invention, the belt has a loop-shaped belt that runs around a first pulley and a second pulley, wherein the first pulley and the second pulley are rotatably mounted about parallel pulley axes, wherein the belt engages with its inner circumference against the outer circumference contours of the pulleys to transmit a torque between the pulleys, wherein in both sections of the belt between the pulleys, a tensioning roller rests against an outer circumference of the belt, wherein the two tensioning rollers are rotatably mounted about roller axes that run parallel to the pulley axes, the two tensioning rollers rest against both pulleys, thus interposing the belt. In other words, in the belt drive according to the invention, the two tensioning rollers act not only on the belt itself but also jointly on the two pulleys.This allows power transmission between the two pulleys and the tensioning rollers without this power transmission occurring along the belt in its main direction of extension. Instead, the power transmission between the tensioning rollers and the pulleys occurs across the thickness of the belt. This means that further approximation of the tensioning roller to the respective pulley is not possible under additional longitudinal tension, but only through deformation of the belt in the thickness direction, where it typically exhibits high stiffness.

[0015] A certain degree of elasticity in the belt's thickness direction can be utilized to compensate for tolerances in that direction. This is achieved by having the tensioning pulley rest against the back of the belt via a contoured outer surface. Depending on the belt's actual thickness, this surface presses into the belt to varying degrees. Specifically, the outer surface of the tensioning pulley can be convex or have several parallel circumferential ribs. Alternatively, the outer surface of the tensioning pulley itself can be elastically deformable to a limited extent.

[0016] In the belt drive according to the invention, the respective tensioning roller can also be positioned both over the belt and directly against the at least one belt pulley, whereby in the area of ​​direct contact there are usually no tolerances to be compensated for, so that it can be a hard contact.

[0017] Due to the supporting effect of the tensioning rollers in the new belt drive, the bearing arrangement of at least one of the two pulleys can be significantly simplified without compromising its stability, which would result in a reversal of direction. This is particularly advantageous in the field of precision mechanics. In fact, at least one of the two pulleys can be rotatably mounted around its axis by the support provided by the two tensioning rollers and the belt itself, eliminating the need for further definition of its axis position, for example, by means of a pivot bearing for a shaft on which at least one of the two pulleys is fixedly mounted.Rather, such a shaft can, for example, be torsionally stiff but flexible, and couple at least one of the two pulleys to an electric motor without requiring the rotor bearing of the electric motor to contribute to or reinforce the rotatable bearing of at least one of the two pulleys, particularly for supporting the belt tension. The load on the bearing of the rotor of an electric motor coupled to a pulley poses a significant problem in known belt drives, especially with wider and correspondingly stiffer belts that require higher tension.

[0018] Furthermore, the positioning of the tensioning rollers on the two pulleys means that the belt tensioned by the pulleys transitions directly from its support by the pulleys to its support by the tensioning rollers, so that no slack is formed in between that could have an effect in the form of a reversal slack.

[0019] Since the two tensioning rollers in the belt drive according to the invention are mounted in stationary rotary bearings, they can support the second pulley in the direction of the first pulley. Because the two tensioning rollers in the belt drive according to the invention bear against both pulleys with intermediate belt positioning, it is sufficient for the roller axes of the two tensioning rollers to have a fixed distance from each other so that the two tensioning rollers support each of the two pulleys in the direction of the other pulley. Furthermore, the bearing of each tensioning roller against each of the pulleys means that the belt does not form any slack in the belt, which could result in a reverse slippage in the belt drive.

[0020] The fixed support of the two tensioning rollers, as well as their fixed distance, does not preclude the possibility that the support exhibits a certain degree of elasticity, for example, due to the bending elasticity of bearing shafts, in order to compensate for tolerances in the belt thickness direction. However, this elasticity is accompanied by high stiffness.

[0021] To achieve the most symmetrical support possible for the two pulleys by the tensioning rollers, these have the same diameter. The wrap angles of the two tensioning rollers with the belt typically range from 60° to 110°. In principle, the wrap angles can also be larger, reaching almost 180°. However, such large wrap angles only occur if a large proportion of the tensioning rollers' cross-sectional area lies between the pulleys, thereby increasing their distance and thus the overall length of the belt, particularly in the areas between the pulleys. This is not advantageous with regard to preventing reversal. Accordingly, the wrap angles of the two pulleys in the belt drive according to the invention are greater than 200°, i.e.,significantly larger than 180°, but typically remain below 270° for the smaller of the two pulleys and rarely exceed 300° for the larger of the two pulleys.

[0022] Preferably, the wheel axes of the two pulleys in the belt drive according to the invention have a minimal distance from each other. Minimal means that any further reduction of the distance between the wheel axes would pose a risk of collision between the rotating pulleys. The two pulleys are therefore separated from each other only by a safety distance in the direction of the distance between their wheel axes. This safety distance is regularly less than one-tenth of the distance between the wheel axes. Often it is less than one-twentieth of the distance between the wheel axes. Only rarely does it exceed one-fifth of the distance between the wheel axes. Because the two pulleys are arranged close together, the belt length is minimized in the areas between the pulleys, and the belt is supported here by the tensioning rollers.

[0023] To change the rotational speed around the wheel axes in the desired direction when transmitting torque between the pulleys—that is, to increase or decrease the speed as needed—the diameters of the outer circumferences of the two pulleys can differ considerably. The outer circumference diameter of the second pulley is at least twice that of the first pulley. The transmission ratio of the belt drive according to the invention is determined by the ratio of these diameters. For the pulley with the larger diameter, the wrap angle of one belt turn, due to the belt being guided between the pulleys by the tensioning rollers, is greater than 270°.

[0024] In one embodiment of the belt drive according to the invention, the first pulley with the smaller diameter is mounted non-rotatably on a drive shaft that can rotate in both directions, while the second pulley with the larger diameter is mounted non-rotatably on an output shaft. The belt drive according to the invention then has a reduction ratio. If the diameter of the outer circumferential contour of the second pulley is at least ten, twenty, or thirty times larger than the diameter of the outer circumferential contour of the first pulley, this reduction ratio is at least 10:1, 20:1, or 30:1, respectively, and thus readily approaches the order of magnitude of tension shaft drives. Nevertheless, a reversal error between the two directions of rotation of the drive shaft is either non-existent or negligibly small in the belt drive according to the invention.

[0025] The diameter of the two tensioning rollers, which bear against the outer circumference of the belt or the pulleys, is preferably 0.5 to 1.5 times the diameter of the outer circumference of the smaller of the two pulleys. Within this diameter range, the length of the belt not bearing against the outer circumference of the pulleys is very short, and the tensioning rollers provide good support for the two pulleys in the direction of the distance between their axes.

[0026] In one embodiment, the belt of the belt drive according to the invention is a toothed belt. Accordingly, the pulleys comprise gears that mesh the toothed belt. Typically, in addition to the gears, the pulleys also include guide discs for lateral guidance of the toothed belt.

[0027] Advantageous further developments of the invention are evident from the claims, the description, and the drawings. The advantages of features and combinations of features mentioned in the description are merely examples and can have an effect alternatively or cumulatively, without necessarily requiring that the advantages be achieved by embodiments of the invention. Without thereby altering the subject matter of the attached claims, the following applies with regard to the disclosure content of the original application documents and the patent: further features can be seen from the drawings—in particular, the geometries and relative dimensions of several components to one another, as well as their relative arrangement and functional connection.The combination of features from different embodiments of the invention or from features of different claims is also possible, deviating from the chosen cross-references in the claims, and is hereby encouraged. This also applies to features that are illustrated in separate drawings or mentioned in their description. These features can also be combined with features from different claims. Likewise, features listed in the claims can be omitted for further embodiments of the invention.

[0028] The features mentioned in the patent claims and the description are to be understood, with regard to their number, as meaning that exactly that number or a greater number than the stated number is present, without the need for the explicit use of the adverb "at least". Thus, for example, if a strap is mentioned, this is to be understood as meaning that exactly one strap, two straps, or more straps are present. These features may be supplemented by other features or may be the only features that the respective product possesses.

[0029] The reference numerals contained in the patent claims do not constitute a limitation of the scope of the subject matter protected by the patent claims. They serve only the purpose of making the patent claims easier to understand. BRIEF DESCRIPTION OF THE FIGURES

[0030] The invention is explained and described in more detail below with reference to a preferred embodiment and the accompanying drawing. Fig. Figure 1 shows a belt drive according to the invention in a sectional view, wherein the section plane is perpendicular to the wheel axes of the belt pulleys of the belt drive. FIGURE DESCRIPTION

[0031] The in Fig. The belt drive 1 shown in Figure 1 has a first pulley 2 that is fixedly mounted on a drive shaft 3, which can be driven to rotate about a wheel axis 4 in both directions. For example, the drive shaft 3 can be an output shaft of an electric motor (not shown). The pulley 2 has an outer circumferential contour 5 for the engagement of a belt 6 in the form of a toothed belt 16. For this purpose, the pulley 2 includes a gear 7 that meshes the toothed belt 16 and is arranged between guide pulleys 8. In addition to the first pulley 2, the toothed belt 16 also engages an outer circumferential contour 9 of a second pulley 10, which also has a gear 11 between guide pulleys 12. The pulley 10 is arranged in a rotationally fixed manner on an output shaft 13, which is rotatably mounted about a wheel axis 14 and which transmits the torque transmitted to the pulley 10 by the belt 6.The two pulleys 2 and 10 have a safety distance 15 between them in the direction of the distance between their wheel axes 4 and 14. Between its contact with the outer circumferential contours 5 and 9, the belt 6 does not run freely, but is directly transferred to a tensioning roller 17, which is rotatably mounted in a rotary bearing 18 about a roller axis 19 that runs parallel to the wheel axes 4 and 14. The tensioning rollers 17 bear against the outer circumference of the belt 6 along its entire length between the pulleys 2 and 10. The diameter of the tensioning rollers 17 is approximately the same as the diameter of the outer circumferential contour of the pulley 2, while the diameter of the outer circumferential contour 9 of the pulley 10 is approximately three times larger than that of the outer circumferential contour 5 of the pulley 2, although significantly larger diameter differences of up to 30:1 and more are also possible. The wrap angle 20 of the belt 6 around the pulley 10 is approximately 300°.The wrap angle 21 of the belt 6 around the pulley 2 is approximately 130°; and the wrap angle 22 of the belt 6 around the tensioning pulleys 17 is approximately 90°. The tensioning pulleys 17 very effectively shorten the lengths over which the belt 6 is not supported against the outer circumferential contours 5 and 9 of the pulleys 2 and 10. They also support the belt 6 over its remaining lengths at its outer circumference. Furthermore, the tensioning pulleys 17 bear against both pulleys 2 and 10 across the belt 6, thus supporting the two pulleys 2 and 10 against each other in the direction of the distance between their wheel axes 4 and 14. This is illustrated by arrows 23 and 24, which show the force transmission from the belt pulleys 2 and 10 to the tensioning rollers 17 when the wheel axles 4 and 14 approach each other, and arrow 25, which shows the counterforce required to support the resultant of these forces.If the distance between the pivot bearing 18 and the roller axles 19 of the tensioning rollers 17 is fixed, the counterforce in the direction of arrows 25 is applied by fastening the pivot bearings 18. The fixed distance between the roller axles 19 and the contact of the tensioning rollers 17 with both pulleys 2 and 10 also ensure that the tensioning rollers 17 cannot move together transversely to the direction of the distance between the wheel axles 4 and 14 when the direction of rotation of the drive of the pulley 2 via the drive shaft 3 is reversed, which would result in a reversal. Such a reversal is not present in the belt drive 1 according to [reference missing]. Fig. 1 rather reliably prevented by the uninterrupted guidance of the belt 6 and the mutual support of the belt pulleys 2 and 10 via the tension rollers 17. REFERENCE MARK LIST 1 Belt drive 2 Pulley 3 Drive shaft 4 wheel axle 5 Outer circumference contour 6 belts 7 gear 8 Guide disc 9 Outer circumference contour 10 Pulley 11 gear 12 Guide disc 13 Output shaft 14 wheel axle 15 safety distance 16 timing belts 17 Tension pulley 18 swivel bearings 19 Roller axle 20 Wrap angles 21 Wrap angle 22 Wrap angles 23 Arrow 24 Arrow 25 Arrow

Claims

[1] Belt drive (1) with a loop-shaped belt (6) which runs around a first pulley (2) and a second pulley (10), wherein the first pulley (2) and the second pulley (10) are rotatably mounted about parallel pulley axes (4, 14), wherein the belt (6) engages with its inner circumference against outer circumferential contours (5, 9) of the pulleys (2, 10) to transmit a torque between the pulleys (2, 10), wherein the belt (6) is a toothed belt (16) and the pulleys (2, 10) comprise gears (7, 11) which mesh the toothed belt (16), wherein in both sections of the belt (6) between the pulleys (2, 10) a tensioning roller (17) bears against an outer circumference of the belt (6), wherein the two tensioning rollers (17) are rotatably mounted about roller axes (19) which are parallel to the Wheel axles (4, 14) run, with the two tension rollers (17) bearing against both belt pulleys (2, 10) under intermediate arrangement of the belt (6),wherein both tension rollers (17) have the same diameter, wherein a diameter of the outer circumferential contour (9) of the second pulley (10) is at least twice as large as a diameter of the outer circumferential contour (5) of the first pulley (2), wherein a wrap angle (20) of a wrap of the second pulley (10) with the belt (6) is greater than 270°, wherein the two tension rollers (17) are mounted in stationary rotary bearings (18), wherein the roller axes of the two tension rollers (17) have a fixed distance from each other, and wherein the two tension rollers (17) support the second pulley (10) in the direction towards the first pulley (2), , characterized by , that the wrap angle (21) of the wrap of the first pulley (2) with the belt (6) is greater than 200° and that the two tension rollers (17) support the first pulley (2) in the direction of the second pulley (10) so that the belt (6) does not form a loose end. [2] Belt drive (1) according to claim 1, characterized by , that the wrap angle (22) of the wraps of the two tension rollers (17) with the belt (6) lies in an angle range of 60° to 110°. [3] Belt drive (1) according to claim 1 or 2, characterized by , that the wheel axles (4, 14) of the two belt pulleys (2, 10) have such a minimal distance to each other that a further reduction of the distance would be associated with the risk of a collision of the belt pulleys (2, 10) rotating about the wheel axles (4, 14). [4] Belt drive (1) according to any one of the preceding claims, characterized by, that the first pulley is mounted non-rotatably on a drive shaft which can be driven in both directions of rotation and the second pulley is mounted non-rotatably on an output shaft, wherein the diameter of the outer circumferential contour (9) of the second pulley (10) is at least ten or 20 or 30 times larger than the diameter of the outer circumferential contour (5) of the first pulley (2). [5] Belt drive (1) according to any one of the preceding claims, characterized by , that the diameter of the two tension rollers (17) is 0.5 to 1.5 times the diameter of the outer circumferential contour (5) of the first pulley (2).

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