driveshaft

Abstract

The present invention provides a drive shaft with a shaft element (4) and a coupling element (2) pivotable relative to the shaft element (4) by means of a rotary joint (2, 4C, 6). The rotary joint has several rolling elements (6) distributed circumferentially, which engage in first recesses (4C) of the shaft element (4) and second recesses of the coupling element (2) in a rotationally fixed, positive-locking coupling such that the shaft element is tiltable relative to the coupling element and the shaft element and the coupling element are essentially rotationally fixed to one another. According to the invention, the shaft element (4) has a flange (4A) directly equipped with the first recesses (4C).This flange (4A) further has several windows (4B) distributed in the circumferential direction, within each of which a fastening element (3) intended for further connecting the coupling element (2) projects.

Description

Technical FieldThe present disclosure relates to a propeller shaft, in particular a balancer shaft, suitable for high rotational speeds. Therefore, a "high-speed" articulated shaft is also referred to.Balance shafts serve to balance an offset between two rotating shafts. The offset can occur radially or in the angular position or in a combination. Two joints are typically installed in a compensation shaft, since one joint alone can only compensate for an angular offset. In order to be able to compensate for a radial offset, two shaft joints are required (i.e. a joint shaft with two joints). A common example of use for compensating shafts is articulated shafts in vehicle axles.The Applicant constructs transmissions for high speed applications, particularly for the development and test fields. In the majority of applications, measurement technology is applied to a fast-running shaft (high-speed shaft) in order to measure or monitor torque and power. For this, there are essentially two possible structures which are schematically depicted as prior art in the enclosed FIGS. 1 and 2. Either (FIG. 1 ) a measuring unit 103 is connected between the drive 101 and the test object 102 via two couplings / articulated shafts 104 to the drive 101 and the test object 102, respectively, or (FIG. 2 ) the measuring flange 203 and the test object 202 are connected via a coupling or articulated shaft 204 and the measuring flange is directly coupled to the drive. Because the coupling / articulated shaft 204 is not mounted separately, a coupling / articulated shaft is omitted in addition to this mounting. As a result, the construction is simpler and also more accurate because of the omitted bearing point. However, the simpler construction according to FIG. 2 is limited in terms of the height of the rotational speeds because of the usually considerable mass of measuring flange 203 and articulated shaft 204, because otherwise the overhanging masses generate rotor dynamic natural frequencies in the operating range. Therefore, two aspects are important here, in particular for high rotational speeds: the articulated shaft should have the lowest possible weight and the centroids of the articulated shaft should be as close as possible to the connection points (and thus at the closest bearing points).In order to be able to achieve the highest possible rotational speeds, both the absolute mass (in order to require less acceleration energy) and, above all, the mass distribution (prevention of imbalance and residual bending frequencies) of the articulated shaft, in particular its connections to the measuring flange and the test object, are therefore of great importance.It is therefore an object of the invention to provide a propeller shaft in which the overall weight is reduced and the weight distribution is optimized for high rotational speeds. In particular, the aim is to place the centroids as close as possible to the bearing points.This object is achieved according to the invention by an extremely slender design of joints of the articulated shaft and a construction of the fastening of the articulated shaft to the screwing-on surfaces which places the centres of mass close to the bearing points.In particular, the present invention provides a articulated shaft having a shaft element and a coupling element which can be pivoted relative to the shaft element by means of a pivot joint. The rotary joint has a plurality of rolling bodies distributed in the circumferential direction. The rolling bodies engage with rotationally fixed positive coupling of the shaft element with the coupling element both in first recesses of the shaft element and in second recesses of the coupling element. According to the invention, the shaft element has a flange directly equipped with the first recesses. This flange further comprises a plurality of windows distributed in the circumferential direction, within which a fastening element intended for further connecting the coupling element extends.Rolling bodies, shaft element and coupling element are located approximately in a plane, the normal of which runs in the axial direction of the articulated shaft. As a result, the shaft element can tilt (slightly) against the coupling element, while both roll on the rolling bodies. In contrast to the prior art, the shaft joint is fastened through the movable joint part of the shaft joint, instead of providing the screw connection on the outside of the hub and thus outside of the shaft joint, as in the prior art. As a result, the diameter of the pitch circle (on which the rolling bodies are arranged) can be made larger than the screw connection diameter. This larger pitch circle results in a greater storage stability and consequently a higher possible rotational speed. Moreover, the mass imbalance of the fastenings located further inward, i.e., closer to the axis of rotation, has less effect on possible imbalance, since the distance from the axis of rotation remains small. Such mass irregularities can never be completely avoided due to manufacturing tolerances and the like.The fastening element is preferably a screw element, wherein the screw element is further preferably manufactured from a light metal, high-strength steel or from fiber-reinforced plastic. In principle, the fastening can also be effected in another manner, for example via locks such as clips and the like, or theoretically also in a force-locking manner, for example by magnetic forces, frictional forces (wherein a normal force could be applied by bracing, as also occurs during screwing) or by adhesion / cohesion (adhesion), welding, riveting, soldering or the like. However, the latter methods which create a non-destructively releasable connection are unsuitable, in particular for changing test setups, and frictional and magnetic forces are hardly able to intercept the counter forces occurring at high rotational speeds. In the case of clips, complicated special constructions are required which are expected to provide little advantages in use; accidental release during operation could lead to imbalance and possibly even to risk of injury due to parts which are thrown away. Screw connections, on the other hand, are proven, favorable and releasable connections with sufficient strength and are therefore preferred in the present case.Further preferably, the screw connection is effected through the shaft flange via bushes. By means of such a measure, the shaft flange can be made thinner or flatter and thus less mass, and the center of mass of the structure can also be brought closer to the hub part. This makes it possible to further reduce vibrations. In addition, the bushings can ensure play between the shaft element and the coupling element, since they do not have to abut both. These bushes are furthermore preferably made of steel, light metal or fiber-reinforced plastic. If the bushes are manufactured from light metal, for example aluminum or titanium, or from plastic, in particular fiber-reinforced plastic, the total mass is further reduced compared to bushes which are manufactured from steel. As a result, the rotational inertia and possible imbalance of the structure can also be further reduced.The rolling elements explained above are preferably rolling balls. Supported on rolling balls, the components of the shaft joint can compensate well for an angular offset of the structure. In addition, rolling balls are favorable and available in practically any dimensions, so that this preferred construction is also readily scalable.Further preferably, the shaft element and the coupling element are connected via a hold-down device which engages around the flange of the shaft element and is fixed to the coupling element by means of further fastening means. In this case, the hold-down device is preferably fixed to the coupling element by means of screws as fastening means and supported via bushes.In a particularly preferred embodiment, the articulated shaft is designed as a constant velocity articulated shaft. Thereby, a rotational motion is uniformly transmitted and thus, no rotational vibrations are generated by the propeller shaft.Brief Description of the FiguresFIG. 1 is a diagram for illustrating a system configuration according to a first prior art; FIG. 2 is a diagram illustrating a system configuration according to a second prior art underlying the present invention; FIG. 3 shows a shaft joint according to the invention in isometric sectional view; FIG. 4 shows an embodiment of the invention in an exploded view; FIG. 5 shows an assembled shaft part according to the invention in a sectional view; and FIG. 6 shows the behavior of the shaft joint according to the invention with torque input, andDESCRIPTION OF THE EMBODIMENTSHereinafter, embodiments of the present disclosure will be described based on the accompanying drawings.In FIG. 1, a (conventional) test setup on a test stand is shown schematically. The drive 101 is mounted in a housing 101A via bearings 101B; opposite it, a test object 102 is likewise mounted in a housing 102A via bearings 102B. A measuring unit 103 is mounted between the device under test 102 and the drive 101 in a housing or a frame 103A via bearings 103B. Clutches 104 are provided both between the drive 101 and the measuring unit 103 and between the measuring unit 103 and the test object 102, which enable a (largely) rotationally fixed connection between the respective parts with simultaneous angle compensation and possibly also length compensation. "Largely" rotationally fixed means that a small (rotational) play can also be possible, for example, when the drive direction is reversed.FIG. 2 shows a schematic test structure of a articulated shaft with a shaft element 204 in which no additional bearing points are required for the measuring unit. In principle, such a construction is also possible with a conventional articulated shaft, but then suffers from the problems explained above for the prior art. In particular, the structure comprises a drive 201 with bearings 201B in a housing 201A, a test object 202 with bearings 202B in a housing 202A, the shaft element 204 and a measurement flange 203 attached directly between shaft element 204 and drive 201. The structure according to FIG. 2 makes it possible to save the frame 103A and the associated bearings 103B compared to the structure according to FIG. 1. Due to the fixed connections between drive 201 and measuring flange 203, between measuring flange 203 and shaft element 204 and between shaft element 204 and test object 202, a more stable force transmission is possible than by means of couplings 104, which is why measuring flange 203 and shaft element 204 do not have to be mounted separately. This lack of bearings analogous to bearings 103B also contributes to a reduction in the masses to be accelerated and possible imbalance at the desired high speeds.As explained above, in this construction in the prior art, the rotational speeds are nevertheless limited due to high masses of the measuring flange and the articulated shaft and imbalance arising as a result during rapid rotation. Here, the present invention starts as shown in FIGS. 3, 4, 5 to 6 explained in more detail below.FIG. 3 schematically shows a three-dimensional section through the inventive shaft joint of a shaft element 4 on a measurement flange (not shown).Fig. 4 shows the construction of the shaft joint according to the invention in an exploded view and Fig. 5 shows the assembled construction in section. The flange hub 2 according to the invention is of flat design; as a result, weight can be saved and the center of mass can be moved closer to the screwing-on surface. More specifically, the shaft flange 4A of the shaft member 4 is provided with through holes or windows 4B through which bolts 3 as fastening members can be passed into bushes 5. The bushings 5 offer the necessary stability in order to securely guide the screw connection in the shaft flange 4A which is made thinner than in the prior art. The bushes 5 preferably consist of steel, but under certain circumstances can consist, for example, of light metal or else of fiber-reinforced plastics in order to achieve a further reduction in weight. In further recesses 4C in the shaft flange 4A, rolling balls 6 are accommodated, which perform a comparable function to the balls 6 explained above. In other words, the rolling balls 6 as rolling bodies form a rotary joint with the flange hub 2 and the recesses 4C located in the shaft flange 4A of the shaft member 4. Rolling balls 6, flange hub 2 and shaft flange 4A are preferably braced against one another, so that the construction is free of play. If a torque is transmitted directly by this play-free arrangement, the joint shaft functions as a constant velocity joint shaft. The screws 3 serve to screw the entire construction to the drive flange (not shown here), for example the drive 201. A hold-down 7 is screwed to the hub part 2 by means of further screws 8, which act as fastening means, and rests on the bushes 5. The hold-down 7 thus engages around the shaft flange 4A and prevents the shaft flange 4A from falling off the hub part 2, Because the shaft flange 4A still has a slight play because of the bushes 5 on which the hold-down 7 rests, despite this fastening, it can tilt on the rolling bodies 6. This ensures the angular mobility (and, in the case of a two-sided construction of the drive and the test object, the articulation of the shaft element).Because no strong forces act on the holding-down device 7 in the axial direction of the structure during testing, it can be screwed to the thin hub part 2 by means of comparatively few, small and light screws 8. As a result, the mass of the structure is further reduced in comparison to the prior art, in particular on the outer periphery.The structure according to the invention arranges the fastening screw connection with the screws 3 within the diameter on which the rolling balls 6 run. Therefore, the relatively solid screws 3 are arranged closer to the central axis of the shaft, so that possible mass differences between screws of the same type due to manufacturing tolerances and the like lead to less imbalance than in the prior art. In addition, due to the possible thinner design of the flanges and the use of the bushings 5, the mass inertia as a whole also decreases. The center of gravity of the shaft joint moves closer to the hub and thus the bearing point, so that possibly still occurring imbalance can also be better absorbed. As a result, it is therefore possible to construct a propeller shaft and a test structure for higher rotational speeds than the structure explained above as the prior art.FIG. 6 shows the behavior of the shaft joint according to the invention with the introduction of torque. As can be seen from the arrows in FIG. 6 which are shown on a rolling body, when a torque is introduced via the shaft flange 4, the latter is pressed onto the rolling bodies 6 which are situated between the shaft flange 4 and the hub part 2. As can also be seen from FIG. 6, these rolling bodies 6 can be arranged without play between the shaft flange 4 and the hub part 2. The torque introduced via the shaft flange 4 thus acts directly on the hub part 2 via the rolling bodies 6 in the embodiment presented here. At the same time, it can be seen from the bushing 5 shown that the bushing 5 is supported on the hub part 2, but, as shown even more clearly in FIG. 5, has a slight play with respect to the shaft flange 4. In addition, the shaft flange around the bushing is designed with a small clearance and is relatively thin. As a result, the shaft flange 4 can tilt relative to the bushing 5, as a result of which the angular offset of the shaft flange 4 and the hub part 2 is made possible. In addition, the masses and thus the inertial forces of the structure are further reduced; at the same time, the frictional connection between shaft flange 4 and hub part 2 via the rolling bodies 6 is maintained even in the tilted state by the prestress explained above. This arrangement further reduces the mass with the same stability.In summary, the invention provides a articulated shaft having a shaft element 4 and a coupling element 2 which can be pivoted relative to the shaft element 4 by means of a pivot joint. The pivot joint comprises the coupling element 2, recesses 4C of the shaft element and a plurality of rolling bodies 6, which are distributed in the circumferential direction and which engage both in first recesses 4C of the shaft element 4 and in second recesses of the coupling element 2 with rotationally fixed positive coupling of the shaft element 4 with the coupling element 2 in such a way that the shaft element 4 can be tilted with respect to the coupling element 2 and the shaft element 4 and the coupling element 2 are connected to one another in a substantially rotationally fixed manner. According to the invention, the shaft element 4 has a flange 4A directly equipped with the first recesses 4C. This flange 4A further has a plurality of windows 4B distributed in the circumferential direction, within which a fastening element 3 intended for further connecting the coupling element 2 projects in each case.

Claims

Articulated shaft having a shaft element (4) and a coupling element (2) which can be pivoted relative to the shaft element (4) by means of a rotary joint (2, 4C, 6), wherein the rotary joint comprises the coupling element (2), recesses (4C) of the shaft element (4) and a plurality of rolling bodies (6) which are distributed in the circumferential direction and engage both in first recesses (4C) of the shaft element (4) and in second recesses of the coupling element (2) with rotationally fixed positive coupling of the shaft element (4) with the coupling element (2) in such a way that the shaft element (4) can be tilted with respect to the coupling element (2) and the shaft element (4) and the coupling element (2) are connected to one another in a rotationally fixed manner, characterized in that the shaft element (4) has a flange (4A) which is directly equipped with the first recesses (4C), wherein this flange (4A) further comprises a plurality of windows (4B) distributed in the circumferential direction, within which a fastening element (3) intended for further connecting the coupling element (2) projects in each case.Articulated shaft according to claim 1, wherein at least one fastening element (3) is a screw (3).Articulated shaft according to Claim 2, wherein the screw (3) is manufactured from a light metal, high-strength steel or from plastic, in particular fiber-reinforced plastic.Articulated shaft according to one of Claims 1 to 3, wherein the flange (4A) is fastened to the coupling element by means of screws (3) which are guided through the flange (4A) in bushes (5).Articulated shaft according to Claim 4, wherein the bushes (5) are manufactured from light metal, high-strength steel or plastic, in particular fiber-reinforced plastic.Articulated shaft according to one of the preceding claims, wherein the rolling bodies (6) are rolling balls.Articulated shaft according to one of the preceding claims, wherein the shaft element (4) and the coupling element (2) are connected via a hold-down device (7) which engages around the flange (4A) of the shaft element (4) and is fixed to the coupling element (2) by means of further fastening means (8).Articulated shaft according to Claim 7, wherein the holding-down device (7) is fixed to the coupling element (2) by means of screws (8) and is supported via bushes (5).The articulated shaft according to one of the preceding claims, wherein the articulated shaft (1) is designed as a constant velocity articulated shaft.Articulated shaft according to one of the preceding claims, wherein the rotationally fixed positive coupling of the shaft element (4) to the coupling element (2) via the rolling bodies (6) is produced by a prestress which clamps the coupling element (2) via the rolling bodies (6) against the shaft element (4).

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