GB2341912A

GB2341912A - Flexible shaft-coupling

Info

Publication number: GB2341912A
Application number: GB9922445A
Authority: GB
Inventors: Kurt Fiedler
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-22
Filing date: 1999-09-22
Publication date: 2000-03-29
Also published as: BR9904291A; GB9922445D0; DE29816999U1; DE19945181A1

Abstract

In a flexible shaft-coupling (10, Fig 1), in particular for the torque-transmitting connection of the facing ends of two substantially aligned shafts of a motor vehicle, at least two anchoring plates 14, 18; 16, 20 each of which can be affixed to a respective shaft end so that viewed in the circumferential direction of the coupling (10), the anchoring plates 14, 18 affixable to one shaft end and the anchoring plates 16, 20 affixable to the other shaft end are arranged alternately. For the transmission of torque, the adjacent anchoring plates 14, 16, 18, 20 are connected to one another by one elastic first strap element 74 and one elastic second strap element 76. The second strap element 76 has a smaller spring constant than the first strap element 74 and the first strap element 74 is only effective from a predetermined angle of torsion between the adjacent anchoring plates.

Description

2341912 Flexible shaft-couDlina The invention relates to a flexible

shaft-coupling, in particular for a motor vehicle, used for the torque-transmitting connection of the facing ends of two essentially aligned shafts, comprising at least two anchoring plates each which can be affixed to each shaft end, wherein, viewed in the circumferential direction of the shaftcoupling, one of the anchoring plates affixable to the one shaft end and one of the anchoring plates affixable to the other shaft end are each arranged alternatingly consecutively, and wherein adjacent anchoring plates are elastically connected to one another by means of one elastic strap element each.

In general, a flexible shaft-coupling serves to connect the facing ends of two shafts in a torsionally elastic manner. The flexible shaft- coupling corrects a possibly existing misalignment between the shafts, compensates for variations in speed and torque between the shafts and prevents the transmission of oscillations between the shafts, which oscillations can have a detrimental influence on the smoothness of running of the shafts. Further, the flexible shaft-coupling is, to a limited extent, also suited to connect shafts to one another which change their relative angular position during operation or which run to one another with a small diffraction angle.

Flexible shaft-coupling are, for example, used in the drive line of a motor vehicle in order to particularly avoid the transmission of occurring torsional oscillations between the shafts. The torsional oscillations are on the one hand caused by variations in torque which result from the gas and mass forces in the combustion engine during the operation of the engine. On the other hand, torsional oscillations in the drive line result from variations in torque acting on the drive wheels during driving due to bumps or different road surfaces. The torsional oscillations in the drive line lead to disturbing noises during driving and cause abrupt loads which might result in the damage of the transmission, the crank shaft of the engine or even the driving shaft of the motor vehicle. In order to disengage the driving wheels and the combustion engine or the transmission with regard to oscillations as well as to compensate for the oscillations in the drive line occurring during driving, the flexible shaft-coupling is arranged between the driven shaft of the differential and the driving shaft of the ganged (i.e. constant- velocity) joint of the driving axle or between the driven shaft of the ganged joint and the shaft butt end of the drive wheel.

From the EP 0 584 821 a flexible shaft-coupling is known, in which occurring torsional oscillations in particular are compensated for with strap elements which elastically connect the shafts for transmitting the torque. For this purpose, the shaft-coupling has two anchoring plates each on each shaft end which can be affixed to each shaft end for example by means of a screw connection. The anchoring plates are arranged such in the circumferential direction of the shaftcoupling that at any one time one of the anchoring plates affixable to one shaft end is adjacent to one of the anchoring plates affixable to the other shaft end. The adjacent anchoring plates are each elastically connected to one another by means of an elastic strap element.

For transmitting the torque, the torque is passed on from the anchoring plates affixed to the driving shaft via the elastic strap elements to the anchoring plates of the shaft that is to be driven. If one of the two shafts starts to oscillate, the strap elements transmit a medium torque of up to 3000 Nm and more, while variations in torque are compensated for between the shafts by the extension or the shortening of the strap elements so that occur-ring torsional oscillations in particular are absorbed. In order to make it possible for the shaft-coupling to absorb the occurring torsional oscillations as completely as possible, the natural frequency of the shaft-coupling, being determined by the mass of the shaftcoupling and the spring constant of the strap elements, is matched with the frequencies of the torsional oscillations generated by the combustion engine and the frequencies of the oscillations usually occurring during driving.

In the case of this flexible shaft-coupling there exists the problem that it has to fulfil two contrasting functions. On the one hand, it has to absorb oscillations within a great range of torques, and on the other hand the spring stiffness of the strap elements must be high enough so that they are able to transmit a torque of up to 3000 Nm. Since, if strap elements are used which do not have a sufficiently high spring stiffness, there is a risk that the anchoring plates hit one another when high torques are applied to the shaft-coupling, and the occurring oscillations can no longer be absorbed. Therefore, the spring constant of the strap elements must not be too small. This, however, has the consequence that, when comparatively small torques are applied to the shaft coupling, the strap elements virtually rigidly connect the shafts due to their high spring stiffness and cannot absorb the occurring oscillations. Thus, in particular for motor vehicles having an automatic transmission, there exists the disadvantage that when changing the gears ' from the neutral gear into one of the other gears, a small torque is suddenly applied to the shaft-coupling first which causes the shaft arrangement to oscillate, and the oscillation cannot be compensated for with the known flexible shaft-coupling for the above- mentioned reasons.

It is the object of the invention to develop a flexible shaft-coupling of the type mentioned at the beginning such that the shaft-coupling sufficiently absorbs the occurring oscillations also when small torques are applied to the shaft-coupling.

In the case of a flexible shaft-coupling of the type mentioned at the beginning, this object is solved by the fact that the respective adjacent anchoring plates are each connected by means of one elastic second strap element for the transmission of torque, and that the second strap element has a smaller spring constant than the first strap element, the first strap element being only effective as from a predetermined angle of torsion between the coupling ends. Preferred developments result from the subclaims.

For the shaft-coupling according to the invention, the torque applied to one of the shafts is only transmitted by the second strap elements until the extension of the second strap elements caused by the torque is so high that the actual angle of torsion between the two coupling ends exceeds the predetermined angle of torsion. Only if this requirement is fulfilled, is the torque transmitted by the second as well as the first strap elements. Since the spring constant and thus the spring stiffness of the second strap elements is smaller as compared to the spring constant of the first strap elements, the second strap elements already extend when a, as compared to the first strap elements, smaller tensile force is generated in the strap elements by the torque. Consequently, the second strap elements can also absorb oscillations occurring in the case of comparatively small torques that are to be transmitted by the shaftcoupling.

The radial distance of the second strap elements to the rotational axis can correspond to the distance of the first strap elements to the rotational axis. Preferably, the radial distance of the second strap elements is however greater so that they can be elongated to a greater extent for the same angle of torsion between the anchoring plates as compared to the first strap elements, and can thus absorb oscillations already in the case of small angles of torsion.

By using strap elements consisting of the same material, different spring constants can be achieved for the first and the second strap elements by making the cross-sectional area of each second strap element perpendicular to the direction of force of the tensile force acting in the second strap element when the torque is transmitted smaller than the corresponding cross-sectional area of each first strap element. In addition, by appropriately selecting the material for the strap elements, the spring constant of the first and the second strap elements, respectively, can be determined. The spring constant of the first strap element should be two to six times higher than the one of the second strap element in order to guarantee that, also in the case of comparatively small torques applied to the shaft-coupling, the occurring oscillations are sufficiently absorbed. This effect can be intensified even more by prestressing the second strap elements in the idle position of the shaft-coupling.

In a preferred embodiment of the shaft-coupling, the anchoring plates which can be affixed to both shaft ends are arranged to one another with the same angular distance with regard to the rotational axis of the shaftcoupling, i.e. that the anchoring plates, which are jointly affixed to one shaft end, are arranged diametrically opposite to one another, while, for example, in the case of a shaftcoupling having three anchoring plates for each shaft end, they are arranged about the rotational axis with a constant angular distance of 120". Due to this kind of arrangement of the anchoring plates with respect to one another it is achieved that the anchoring plates and the strap elements are exposed to torques which are at least almost equal.

In addition, it is advantageous if the anchoring plates are arranged with at least almost equal radial distance to the rotational axis of the shaftcoupling, whereby it is also achieved that almost the same torques are applied to the anchoring plates and the strap elements.

In order to reduce the occurring oscillations, it is advantageous to form the shaftcoupling such that it not only compensates for but also damps the oscillations. For this purpose, in a preferred embodiment of the shaft-coupling, the anchoring plates are at least in the area of the first and second strap elements surrounded by an elastomer which is rigidly connected to the anchoring plates, and the strap elements are embedded in the elastomer. While the strap elements compensate for the occurring oscillations, the elastomer at least partly absorbs the generated oscillation energy and damps the oscillations. Suitable examples for elastomers are natural or synthetic rubber compounds which are applied to the shaft-coupling after the assembly of the anchoring plates and the strap elements and which are afterwards rigidly connected thereto by means of vulcanizing.

Endless coil springs are suitable as strap elements which are rigidly connected to the anchoring plates. Alternatively, resilient rings can also be used as strap elements which are affixed to the respective adjacent anchoring plates and elastically connect these to one another. In a preferred embodiment of the shaftcoupling anchoring pins are provided on each anchoring plate, the anchoring pins of respective adjacent anchoring plates projecting in at least almost the same direction. As first strap element an elastic oval ring is used which is mounted on the two anchoring pins such that it elastically connects the pair of adjacent anchoring plates to one another. Since the elastic rings only have to be mounted on the anchoring pins for elastically connecting the anchoring plates to one another, the assembly of the shaft-coupling has been simplified.

In one development of this preferred embodiment a bolt is projecting from each anchoring pin of each pair of adjacent anchoring plates, the longitudinal direction of said bolt extending at least almost parallel to the longitudinal direction of the anchoring pin from which it projects. The second strap elements are also formed as elastic rings, wherein each ring forming a second strap element is mounted on the parallel extending bolts of each pair of adjacent anchoring plates, and elastically connects the two anchoring plates to one another.

The elastic first rings, which are used as first strap elements, are preferably formed as thread packages, which are each wound round the two anchoring pins of the relevant pair of adjacent anchoring plates in the form of an oval or an eight. Accordingly, the second rings forming the second strap elements can also be formed as thread packages which are wound round the bolts of each of adjacent anchoring plates. The thread of each elastic first ring from which the thread package has been wound, has a breaking elongation in the range of about 4 to 5%. In contrast thereto, a thread is used for the thread package of each elastic second ring, the breaking elongation of which is in the range of about 15 to 25%.

This guarantees that the elasticity of the second rings forming the second strap elements is higher and thus the spring constant of the second rings is smaller than the one of the first rings.

As basic material for the first ring preferably a thread is used which consists at least partly of aramid, since aramid can resist very high tensile forces as compared to other synthetic fibers. The thread of each elastic second ring is at least partly made of rayon or nylon, both having a tensile strength smaller than the one of aramid, but a comparatively high elasticity.

Instead of thread packages also packages wound of metal wire can be used, however, when selecting the material for the metal wire attention has to be paid to a sufficiently high tensile strength on the one hand and a sufficiently high elasticity on the other hand.

In order to further reduce the axial overall length of the shaft-coupling, while preventing a torsion of the adjacent anchoring plates beyond a predetermined angle of torsion, the anchoring plates are formed such in a preferred embodiment that two adjacent anchoring plates each overlap one other in the radial plane and engage behind one another in the direction of the rotational axis in sections, so that a substantially Z-shaped gap is formed between the anchoring plates. If the anchoring plates are moved against one another up to a predetermined angle of torsion, they abut one another, due to the fact that they are engaged behind one another, whereby a further movement of the anchoring plates is prevented so that the outer second strap elements are not overloaded in the case of extremely high torques.

In a development of this preferred embodiment, a damping element is arranged in the Z-shaped gap formed between the two adjacent anchoring plates, said damping element being rigidly connected to at least the facing surfaces of the two adjacent anchoring plates so that the shaftcoupling not only absorbs but also damps the oscillations by means of the strap elements. As damping element an elastomer in particular can be used such as a natural or synthetic rubber compound, said elastomer being rigidly connected to all facing surfaces of the anchoring plates.

In order to be in defined position even in an unassembled state of the shaftcoupling, the anchoring plates are arranged such about the rotational axis that they form a clearance concentrically surrounding the rotational axis, in VAch clearance a centering element having at least a partly cylindrical surface area, such as a bush, is inserted, on the circumferential surface thereof the anchoring plates which are elastically prestressed by the strap elements being supported.

In addition, the centering element can have a collar on its circumferential surface which projects radially outwardly and which engages with at least one elevation which is formed by the internal circumferential surfaces of the anchoring plates forming the circumferential edge of the clearance, thus preventing an axial displacement of the anchoring plates.

Brief DescriRtion of the Drawings In the following the invention is explained in more detail on the basis of one embodiment with reference to the enclosed drawing.

Figure 1 is a top view of a flexible shaft-coupling, Figure 2 is a top view of the flexible shaft-coupling, the elastomer jacket having been omitted, Figure 3 is a top view of one of the anchoring plates of the flexible shaft-coupling, Figure 4 is a rear view of the anchoring plate according to Figur 3, Figure 5 is a sectional view of the flexible shaft-coupling taken along the line V-V, illustrating a centering bush supporting the anchoring plates, Figure 6 is a sectional view of the flexible shaft-coupling taken along the line VIVI, illustrating a radial gap between the anchoring plates, Figure 7 is a sectional view of the flexible shaft-coupling taken along the line V11VII, illustrating a Z-shaped gap between the anchoring plates, and Figure 8 is a diagram illustrating the spring constants of the various thread packages, of the coupling body and of the flexible shaft-coupling as well as the spring constant resulting from the spring constants of the second thread package and of the coupling body as a function of the torsional torque.

Figure 1 is a top view of a flexible shaft-coupling 10 with which, for example in a motor vehicle, the driven shaft of a differential and the driving shaft of a ganged joint of the drive axle are connected to one another for transmitting torque. The shaft-coupling 10 has a coupling body 12 made of an elastomer into which four identical anchoring plates 14, 16, 18 and 20 are embedded, as shown in Figure 2, in which the coupling body 12 of the shaft-coupling 10 is only illustrated in broken lines. Next, for a better understanding, the anchoring plate 14 is described in more detail with reference to the Figures 3 and 4.

The anchoring plate 14 is formed of a plate 22 in the shape of a cuboid having a substantially square base. In the center of the square base of the plate 22 a through hole 24 is formed which extends between the front side 26 (see Figure 3) and the rear side 28 (see Figure 4) of the plate 22 and through which a threaded bolt (not shown) can be inserted in order to affix the anchoring plate 14 to one end of one of the shafts that are to be connected. As shown in Figure 3, an annular recess 30 is formed on the front side 26 of the plate 22, said recess 30 being arranged concentrically to the through hole 24 and serving as support surface for the threaded head of the threaded bolt. On the rear side 28 of the plate 22, which is shown in Figure 4, an annular elevation 32 is formed concentrically to the through hole 24, the surface of said elevation being knurled and serving as support surface for the end of the shaft.

From the lateral surface 34 of the plate 22, shown on the right hand side in Figure 3, a first anchoring pin 36 projects which is formed of a semicylindrical section 38 and a section 40 in the shape of a cuboid adjacent to the section 38. The semicylindrical section 38, which is arranged with its longitudinal axis approximately centrical with regard to the lateral surface 34 and projects therefrom with its longitudinal direction points, with its curvature, in the direction of the second lateral surface 42 of the plate 22 and has a radially projecting collar 44 on its end face. The side of the semi -cylindrical section 38 facing away from the curvature joins the cuboid-shaped section 40, the lateral edges of which extending parallel to the front side 26 or rear side 28 are flattened. Further, a cylindrical first bolt 46 -g- projects from the end face of the semi-cylindrical section 38 of the first anchoring pin 36, the longitudinal axis of said bolt 46 coinciding with the longitudinal axis of the semi-cylindrical section 38.

On the second lateral surface 42, shown at the bottom in Figure 3, a second anchoring pin 48 is provided, the structure of which substantially corresponds to the structure of the first anchoring pin 36 and the curvature of which points in the direction of the first lateral surface 34. On its end face the second anchoring pin 48 supports a cylindrical second bolt 50, the longitudinal axis of which also coincides with the longitudinal axis of the semi-cylindrical section of the second anchoring pin 48.

On the third lateral surface 52, shown on the left hand side in Figure 3, there is a first projection 54 which on the one hand joins the front side 26 of the plate 22 and on the other hand the cuboid-shaped section of the second anchoring pin 48, the first projection 54 being flush with the end face of the second anchoring pin 48. The bottom side of the projection running parallel to the rear side 28 of the plate is set back and forms together with the third lateral surface 52 and the rear side 28 of the plate 22 a shoulder, as shown in Figure 4. Further, the first projection 54 is shortened in the direction of the third lateral surface 52 so that a recess 56 is formed which is formed approximately opposite of the first anchoring pin 36.

In the area of this recess 56, a second projection 58 projects from the third lateral surface 52, which projection 58 joins the rear side 28 of the plate 22 and which is set back with its bottom side running parallel to the front side 26 of the plate 22 in such a way that it forms a shoulder with the third lateral surface 52 and the front side 26 of the plate 22. On its end face pointing towards the fourth lateral surface 60 of the plate 22, the second projection 58 is rounded and joins a third projection 62 projecting from the fourth lateral surface 60, said projection 62 joining the rear side 28 of the plate 22 and the lateral edges of the cuboid-shaped section 40 of the first anchoring pin 36 and being flush with the end face of the first anchoring pin 36. The end face of the third projection 62 pointing towards the third lateral surface 52 is also rounded and forms together with the end face of the second projection 58 a support surface 64 having a constant radius of curvature, the purpose of which will be explained later on.

As shown in Fig. 2, the anchoring plates 14, 16, 18 and 20 are alternatingly arranged next to each other with their front sides 26 and their rear sides 28 such that two anchoring plates 14 and 18, and 16 and 20, respectively, poinfing in' the same direction with their front sides 26 and their rear sides 28, respectively, are diametrically opposite to one another. When the shaft-coupling 10 is affixed to the ends of the shafts that are to be connected, the diametrically opposite anchoring plates 14 and 18, and 16 and 20, respectively, are each affixed to a common shaft end so that for example the anchoring plates 14 and 18 arranged on the upper left side and the lower right side in Figure 2 are affixed to the end of the one shaft, and the anchoring plates 16 and 20 illustrated on the lower left side and the upper right side in Figure 2 are affixed to the end of the other shaft.

Due to this kind of arrangement of the anchoring plates 14, 16, 18 and 20 with respect to each other, the anchoring plate 14, for example, engages with its first and second projections 54 and 58 behind the first and second projections of the anchoring plate 20 arranged on its right hand side, while it engages with its third projection 62 behind the third projection of its adjacent other anchoring plate 16. In addition, the first anchoring pin 36 of the anchoring plate 14 points in the same direction as the first anchoring pin 36' of the anchoring pin 16, while the second anchoring pin 48 of the anchoring plate 14 points in the same direction as the second anchoring pin 48' of the anchoring plate 20.

In order to space the anchoring plates 14, 16, 18 and 20 apart from one another, they are jointly arranged about the rotational axis of the shaftcoupling 10 in such a way that their support surfaces 64 form a clearance into which a centering bush 66 is inserted on which the anchoring plates 14, 16, 18 and 20 are supported in radial direction with their support surfaces 64, as shown in Figure 2 in connection with the sectional view taken along the line V-V in Figure 5 and the sectional view taken along the line VINI in Figure 6. In order to support the anchoring plates 14, 16, 18 and 20 also in the axial direction, the centering bush 66 further has a circumferential bush collar 68 on its outer surface area, on which the second and third projections 58 and 62 of the anchoring plates 14, 16, 18 and 20 abut.

Due to this type of support of the anchoring plates 14, 16, 18 and 20 on the centering bush 66, a radially extending gap 70 is formed between the anchoring plates 14, 16, 18 and 20, as shown in Figure 6, said gap allowing a movement of the pair of anchoring plates 14 and 18 towards the pair of anchoring plates 16 and in the axial direction of the shaft-coupling 10. Further, as shown in Figure 7, a Z-shaped gap 72 is formed between the first and second projections 54 and 58 as well as between the third projections 62 of the respective adjacent anch6ring plates 14, 16, 18 and 20, said gap allowing a movement of the pair of anchoring plates 14 and 18 towards the pair of anchoring plates 16 and 20 in the axial direction. In order to rigidly connect the anchoring plates 14, 16, 18 and 20 to one another, the gaps 70 and 72 are filled with the elastomer of the coupling body 12, said elastomer being scorched at the flat surfaces of the anchoring plates 14, 16, 18 and 20 forming the gaps 70 and 72.

As shown in Figure 2, first thread packages 74 in the form of an oval are each mounted around the first anchoring pins 36 and 36' and the second anchoring pins 48 and 48', each pointing in the same direction, respectively, in order to elastically connect the respective adjacent anchoring plates 14, 16, 18 and 20. The first thread packages 74 are each formed of an aramid thread, which is wound round the anchoring pins 36 and 36' and 48 and 48', respectively, without any prestressing with 120 turns in 12 rows and 10 layers in such a way that the pair of anchoring plates 14 and 18 can be swivelled relative to the pair of anchoring plates 16 and 20 round an angle of torsion of 1,5", until the first thread packages 74 become effective as to the transmission of torques as will be described in more detail further below with reference to Figure 8. The collar 44 formed on the anchoring pins 36 and 36, and 48 and 48', respectively, prevents a loosening of the first thread packages 74 in the idle position of the shaft-coupling 10.

In the same manner, one second thread package 76 in the form of an oval is each mounted around the first bolts 46 and 46' as well as the second bolts 50 and 50' of the respective adjacent anchoring plates 14, 16, 18 and 20, the first bolts and the second bolts each pointing in the same direction. A sleeve 78 mounted on each of the bolts 46 and 46' as well as 50 and 50' prevents a loosening of the respective second thread package 76 from the respective bolts 46, 46', 50 and 50'. The second thread packages 76 are each formed of a rayon thread which is wound with prestressing with 30 turns, in 10 rows and 3 layers round the sleeves 78 which are slipped over the bolts 46 and 46' pointing in the same direction and the bolts 50 and 50' also pointing in the same direction. By means of the prestressing of the second thread package 76 caused by the winding, it is achieved that the anchoring plates 14, 16, 18 and 20 are kept in a defined position and are supported on the centering bush 66 with a predetermined force by means of their cylindrical support surfaces 64. As also shown in Figure 6, the thread packages 74 and 76 are embedded into the elastomer material of the coupling body 12.

The transmission of the torque is effected in the shaft-coupling 10 by means of the coupling body 12 and the thread packages 74 and 76. In the following, the function of the flexible shaft-coupling 10 is explained in more detail with reference to Figure 8. Figure 8 shows a diagram in which the spring constants C, and C2 Of the thread packages 74 and 76, the spring constant CE of the coupling body 12, the resulting spring constant CE+2 of the spring constants C, and CE as well as the total spring constant CE+1+2 of the shaft-coupling 10 are illustrated as a function of the torque applied to the shaft-coupling 10 and the angle of torsion between the anchoring plates 14 and 18 as well as 16 and 20.

As shown by the spring constant C2 of the second thread packages 76illustrated in Figure 8, the thread packages 76 are prestressed by the winding round the bolts 46 and 46' as well as 50 and 50' so that a static torque of approximately 150 Nm acts on the thread packages 76 already in the idle position, i.e. at a angle of torsion of 0. Thus, it is achieved that already in the case of small torques being applied to the shaftcoupling 10, said torques effecting a relative movement of the anchoring plates 14, 16, 18 and 20 with respect to one another, the thread packages 76 are elongated.

If, for example, a torque of about 300 Nm is applied to the shaftcoupling 10, it will first be transmitted by the second thread packages 76 mounted on the bolts 46 and 46' as well as 50 and 50' of the anchoring plates 14, 16, 18 and 20 and the coupling body 12. The coupling body 12 and the second thread packages 76 elongate according to their respective spring constant CE and C2 and the applied torque so that the pair of anchoring plates 14 and 18, which is affixed to the end of the one shaft, is twisted relative to the pair of anchoring plates 16 and 20 which is affixed to the end of the other shaft about an angle of torsion of 1 ". If variations in torque occur on one the two shafts which result in an oscillation of the shaft, the additional relative movements between the anchoring plates 14 and 18 as well as 16 and 20 caused by the oscillations are absorbed by the second thread packages 76, which either extend or shorten themselves in accordance with the relative movements and thus prevent a transmission of the oscillation movement to the other shaft, while the elastomer material of the coupling body 12 concurrently damps the oscillations.

If the torque applied to shaft-coupling 10 exceeds 500 Nm so that the angle of torsion between the pair of anchoring plates 14 and 18 and the pair of anchoring plates 16 and 20 is greater than or equal to 1,W, the applied torque is transmitted, in addition to the second thread packages 76, also by the first thread packages 74 mounted on the anchoring pins 36 and 36' as well as 48 and 48', said first thread packages only becoming effective as from this angle of torsion since they are loosly wound round the anchoring pins 36 and 36' and 48 and 48', respectively.

As can be seen from the diagram in Figure 8, the spring constant Cl of the first thread packages 74 is four times higher as compared to the spring constant C2 of the second thread packages 76 so that the first thread packages 74 do extend or shorten jointly with the second thread packages 76 in accordance with the torque applied to the shaft-coupling 10, but oppose more force to the torsion of the pair of anchoring plates 14 and 18 relative to the pair of anchoring plates 16 and 20. Thus, a transmission of the oscillations between the shafts is prevented, while the elastomer material of the coupling body 12 concurrently damps the oscillations. At the same time, the first thread packages 74, the aramid thread of which has a higher tensile strength than the rayon thread of the second thread packages 76, prevent that the second thread packages 76 are damaged by the high torque applied. Thus, a total spring constant CE+ 1+2 composed of the spring constants Cl and C2 of the first and second thread packages 74 and 76 and the spring constant CE of the coupling body 12 results for the shaft-coupling 10, said total spring constant having an influence on the relative movement between the pairs of anchoring plates 14 and 18 as well as 16 and 20 and being only effective as from an angle of torsion being greater than 1,5".

In the case of the shaft-coupling 10 oscillations occurring at small torques are first compensated for with the second thread packages 76 and are damped by the coupling body 12. Only if the torque applied to the shaft-coupling 10 exceeds a value causing a relative movement between the pairs of anchoring plates 14 and 18 as well as 16 and 20, the angle of torsion of which being greater than 1,W, the first thread packages 74 will become effective and transmit the torque jointly with the second thread packages 76. Thus, it is achieved that the shaft-coupling 10 can compensate for oscillations between the shafts already occuring in the case of comparatively small torques.

Claims

Claims

Flexible shaft-coupling, in particular for a motor vehicle, used for the torq'uetransmitting connection of the facing ends of two essentially aligned shafts, comprising at least two anchoring plates each which can be affixed to each shaft end, wherein, viewed in the circumferential direction of the shaftcoupling, one of the anchoring plates affixable to the one shaft end and one of the anchoring plates affixable to the other shaft end are each arranged alternatingly consecutively, and wherein adjacent anchoring plates are elastically connected to one another by means of one elastic strap element each, characterized in that the respective adjacent anchoring plates are connected to one another by means of one elastic second strap element each for transmitting the torque, and that the second strap element has a smaller spring constant than the first strap element, the first strap element being only effective as from a predetermined angle of torsion between the coupling ends.
2. A flexible shaft-coupling according to claim 1, characterized in that the radial distance of the second strap element to the rotational axis of the shaftcoupling is greater than the. one of the first strap element.
3. A flexible shaft-coupling according to claim 1 or 2, characterized in that the cross-sectional area of the second strap element perpendicular to the direction of force of the tensile force acting in the second strap element when the torque is transmitted is smaller than the corresponding crosssectional area of the first strap element.
4. A flexible shaft-coupling according to claim 1.. 2 or 3, characterized in that the spring constant of the first strap element is two to six times greater than the one of the second strap element.
5. A flexible shaft-coupling according to one of the claims 1 to 4, characterized in that the second strap element is prestressed in the idle position of the shaft-coupling.
6. A flexible shaft-coupling according to one of the claims 1 to 5, characterized in that the anchoring plates are arranged about the rotational axis of the shaft-coupling with the same angular distance with respect to one another.
7. A flexible shaft-coupling according to one of the foregoing claims, characterized in that the anchoring plates have at least almost the same radial distance to the rotational axis of the shaft-coupling.
8. A flexible shaft-coupling according to one of the foregoing claims, characterized in that the anchoring plates are surrounded at least in the area of the first and second strap elements by an elastomer which is rigidly connected to the anchoring plates, and that the anchoring plates are embedded into the elastomer.
9. A flexible shaft-coupling according to one of the foregoing claims, characterized in that an anchoring pin projects from each of the respective adjacent anchoring plates in at least almost the same direction, and that each first strap element is an elastic oval first ring, which is mounted on the two anchoring plates such that it elastically connects the pair of adjacent anchoring plates to one another.
10. A flexible shaft-coupling according to claim 9, characterized in that a bolt is projecting from each anchoring pin of each pair of adjacent anchoring plates, the longitudinal direction of said bolt extending at least almost parallel to the longitudinal direction of the anchoring pin from which it projects, and that the second strap element is an elastic second ring, which is mounted on the parallel extending bolts of each pair of adjacent anchoring plates such that it elastically connects the two anchoring plates to one another.
11. A flexible shaft-coupling according to claim 9 or 10, characterized in that each elastic first ring and/or each elastic second ring is formed of a thread package, which is each wound round the two anchoring pins or the two bolts of the respective pair of adjacent anchoring plates in the form of an oval or an eight.
12. A flexible shaft-coupling according to claim 11, characterized in that the thread of each elastic first ring has a breaking elongation in the range of approximately 4 to 5%, and the thread of each elastic second ring has a breaking elongation in the range of approximately 15 to 25%.
13. A flexible shaft-coupling according to claim 12, characterized in that the thread of each elastic first ring is made at least partly of aramid, and the thread of each elastic second ring is made at least partly of rayon or nylon.
14. A flexible shaft-coupling according to one of the foregoing claims, characterized in that the respective two adjacent anchoring plates overlap one another in the radial plane and engage behind one another in the direction of the rotational axis in sections so that a substantially Z-shaped gap is formed between the anchoring plates.
15. A flexible shaft-coupling according to claim 14, characterized in that a damping element is arranged within the Z-shaped gap formed between the two adjacent anchoring plates, said damping element being rigidly connected to at least the facing surfaces of the two adjacent anchoring plates.
16. A flexible shaft-coupling according to claim 15, characterized in that the damping element is formed of an elastomer which is rigidly connected to all facing surfaces of the anchoring plates.
17. A flexible shaft-coupling according to one of the foregoing claims, characterized in that the anchoring plates are arranged about the rotational axis such that they form a clearance concentrically surrounding the rotational axis, into which clearance a centering element having an at least partly cylindrical surface area is inserted and on the circumferential surface of which the anchoring plates being elastically prestressed by the strap elements are supported.
18, A flexible shaft-coupling according to claim 17, characterized in that the centering element has a radially outwardly projecting collar on its circumferential surface which engages with at least one elevation which is formed by the internal circumferential surfaces of the anchoring plates forming the circumferential edge of the clearance.
19. A flexible shaft-coupling substantially as hereinbefore described with reference to and as shown in the accompanying drawings.