GB2028970A

GB2028970A - Leaf spring couplings

Info

Publication number: GB2028970A
Application number: GB7927833A
Authority: GB
Original assignee: Voith Getriebe KG
Current assignee: Voith Getriebe KG
Priority date: 1978-08-26
Filing date: 1979-08-09
Publication date: 1980-03-12
Also published as: GB2028970B; ATA521779A; FR2434304A1; IT7968715A0; SE437414B; SE7907038L; AT384085B; IT1203302B; FR2434304B1

Abstract

A leaf spring coupling comprises an inner coupling half 21 and an outer coupling half 22 inter-connected rotationally and resiliently by radially arranged sets 23 of leaf springs each set of which, in the form of a body with uniform bending stress, has various lengths of leaf springs, such that the longest leaf springs 30 ("main springs") have a plurality of flanking springs 31, 32, 33 and 36, 37, 38 appertaining to them, the length of which decreases stepwise from spring to spring, the sets of leaf springs being clamped in one of the coupling halves and engaging via their main springs in the other coupling half. An object of the invention is to develop this kind of coupling so that its characteristic curve is as nearly as possible a smooth progressive path. The invention is characterised in that the other coupling half has stops 41, 42, 43 and 46, 47, 48 for the transmission of torque which are arranged to engage with at least some of the flanking springs, after a certain angle of torsion has been reached; alternatively the stops may be formed as a smooth curve. <IMAGE>

Description

SPECIFICATION Leaf spring coupling The invention relates to a leaf spring coupling of the kind having an inner coupling half (hub) and an outer coupling half (outer ring), which are interconnected rotationally and elastically via radially arranged sets of leaf springs which, in the form of a body with uniform bending stress, have variously long leaf springs, such that the longest leaf springs ("main springs") have a plurality of socalled flanking springs appertaining to them, the length of which decreases stepwise from spring to spring, the sets of leaf springs being clamped in one of the coupling halves and engaging via their main springs in the other coupling half.

In a known coupling of this kind (see the publication Kupplungs-Atlas, 1975, pages 40 and 41, A.G.T.-Verlag Georg Thumm, Ludwidsburgj the sets of leaf springs are clamped in on the outer ring using intermediate elements which extend between the sets of leaf springs in the direction of the hub. On their radially inner end the intermediate elements have abutment surfaces via which they rest against those leaf springs which engage in the hub, thus the so-called main springs, at the maximum angle of torsion set in any given case. The terminal stop thus formed is hard, and the main springs are subjected during this abutment to great shearing stresses. As a result, there is a danger that the main springs wili break during severe torque shocks.

The rigidity of the known coupling is constant up to the terminal abutment, i.e. its characteristic coupling curve rises linearly. However, it is often necessary for the torsional rigidity to increase progressively with increasing angle of torsion. For this purpose, a coupling has already been proposed in which only some of the sets of leaf springs are constantly engaged in the other half of the coupling, whilst the others do not engage until after a specific angle of torsion has been reached.

In this way a characteristic curve is created which has two linear regions with different slopes. Thus, this characteristic curve already approaches a progressive characteristic curve, and can be designated a "phased progressive characteristic curve", but the phasing is still very rough, and oscillation problems can result from this. In addition, it is unsatisfactory that some of the sets of leaf springs only participate intermittently in the transmission of torque, i.e. these sets of leaf springs are ineffective below the angle of torsion at which they become engaged.

An object of the invention is to develop the known leaf spring coupling described hereinbefore in such a way that its characteristic curve approaches as nearly as possible a smooth progressive path, while uniform use of the sets of leaf springs is retained.

According to the invention a leaf spring coupling of the kind referred to hereinbefore is characterised in that the other coupling half has stops for the transmission of torque which are arranged to engage with at least some of the flanking springs, after a certain angle of torsion has been reached.

With the known leaf spring couplings, during the transmission of force in one circumferential direction, only the so-called front flanking springs are brought into use for the transmission of force, by supporting the main springs. Meanwhile, the so-called rear flanking springs remain unloaded.

(For this reason, moreover, in some of the known leaf spring couplings the rear flanking springs are entirely or partly omitted). On the other hand, the leaf spring coupling according to the invention is distinguished by the fact that at least some of the rear flanking springs can be used additionally for the transmission of force, since these flanking springs co-act with stops on the other coupling half when a certain angle of torsion is exceeded. in this way, according to the fineness of the graduation of the flanking springs, a more finely or less finely graduated progressive characteristic curve and a relatively softer final abutment is obtained, the high shearing stress on the main springs thus being avoided.Further, due to the cooperation of the rear flanking springs and due to the fact that even at small angles of torsion all the sets of springs participate in the transmission of force, the greatest possible exploitation of the leaf springs is achieved. This means that, for a specific maximum torque, the coupling can either be made smaller than hitherto, or the number of sets of leaf springs can be reduced, Advantageous developments and various modified versions of the leaf spring coupling according to the invention are covered by the subsidiary Claims. The greater the number of flanking springs to which one stop appertains, the higher is the level of efficiency of the leaf springs as a whole (Claim 4). In addition, with the characteristics in Claim 5 particularly fine phasing of the increase in torsional rigidity of the coupling is achieved as the torsional angle becomes greater.In Claims 6 and 7 two different construction examples of the invention are indicated. Here, the second differs from the first mainly by a more steeply rising characteristic curve, assuming that identical leaf springs are used. In this case, provision is made for the radius of the application of force to become increasingly smaller as the angle of torsion becomes larger, with engagement of the rear leaf springs, Conversely, in the embodiment according to Claim 6 provision is made for the flanking springs to come into the engaged state at relatively short intervals. This means that the rear flanking springs act first as individual springs, i.e. they do not come into contact with the rest of the set of springs.In this instance, and also when all the leaf springs are resting on each other at the maximum angle of torsion, the abutment surfaces are evenly loaded, as in the version according to Claim 7, so that reduced wear may be anticipated.

By varying the thickness of the spring plate (Claim 9), the characteristic curve of the coupling can be influenced. However, in addition, in the embodiment according to Claim 10, it is possible to obtain the same bending stress in the clamping zone for all the springs. Moreover, the stops can be designed so that for an individual set of leaf springs an arc-shaped bending line can be enforced (Claim 11). In this way, it is possible to ensure that at least approximately the same bending stresses prevail in all areas of the set of springs.

With the coupling according to the invention, the sets of leaf springs can either be clamped in the outer ring (as known from the publication Kupplungs-Atlas referred to hereinbefore ar in the hub (as known from German Patent Specification No. 555 438). However, the latter arrangement is more advantageous (Claim 13), since in thins case the stops are formed by segment-type sections of the outer ring, which for this purpose extend radially inwards into the zones located between the sets of leaf springs. If the coupling has side discs (so that the inner volume of the coupling can be filled with lubricating medium) these side discs can also be attached to the segment-type sections of the outer ring, thus not only on its outer circumference. The additional fixing means (e.g.

screws) can in this case be arranged relatively close to the hub, as is known from the Kupplungs Atlas. This means that when provision is made for filling with fluid, the stresses which arise due to the fluid pressure on the side discs can be better controlled.

Another important advantage of the invention consists in the following: if a reduced number of sets of leaf springs is used and if these are clamped in at the hub, space is gained at the hub for a particularly strong construction of the clamping components. In an expedient embodiment of the invention these can be constructed according to Claims 14 to 17.

Construction examples of the invention are described in the following with reference to the Drawing.

Figure 1 is a partial cross-section through a leaf spring coupling.

Figures 2 to 5 show a set of leaf springs from the coupling shown in Figure 1, at different angles of torsion.

Figures 6 to 9 show a set of leaf springs from another coupling, also at different angles of torsion.

Figure 1 0 shows the characteristic curve of the coupling shown in Figures 1 to 5.

Figure 11 shows the characteristic curve of the coupling shown in Figures 6 to 9.

Figures 12 and 13 show a set of leaf springs of another coupling in the unloaded and the maximally loaded state respectively.

Figure 14 shows a modified version of a set of leaf springs.

The rotationally elastic coupling, constructed as a leaf spring coupling, shown in Figure 1 and designated 20 as a whole, comprises basically a hub 21 (as the inner coupling half), and an outer ring 22 (as the outer coupling half), with a connecting flange 22a and a plurality of sets 23 of leaf springs which are clamped in at the hub 21 and extend in the radial direction into recesses 26 in the outer ring 22. To clamp in the sets 23 of leaf springs at the hub 21 wedge-shaped intermediate elements 24 and 25 are provided, tapering in the direction towards the axis of the coupling. In the circumferential direction of the hub 21 , fixed intermediate elements 24 integral with the hub alternate with separate intermediate elements 25 which are bolted onto the hub.This is a simple, space-saving and yet secure fixing for the sets 23 of leaf springs on the hub 21.

Each of the sets 23 of leaf springs has variously long leaf springs in the form of a body with the same bending stress. Preferably with a symmetrical arrangement, in the centre of the set of leaf springs the longest leaf springs 30, which are also called main springs, are arranged. On either side of these several so-called flanking springs 31, 32, 33 and 36, 37,38 are arranged, the length of which decreases stepwise from spring to spring.

The recesses 26 provided in the outer half of the coupling, i.e. in the outer ring 22, are shaped as follows: in their radially outer zone they form grooves 27 which extend axis-parallel, and the width of which is only slightly greater than the total thickness of the main springs 30. The main springs 30 are therefore constantly engaged with the outer coupling half. A certain amount of play between the main springs 30 and the side faces of the groove and their rounded shape ensures that there is no jamming during mutual twisting of the two halves 21 and 22 of the coupling.

Each of the flanking springs 31, 32, 33 and 36, 37, 38 has an abutment surface appertaining to it, which has a reference numeral 10 higher than that of the leaf springs. The transitions between these abutment surfaces and from the abutment surfaces to the groove 27 are rounded so that the boundary wall of the whole recess 26 is undulating.

Figure 1 shows the coupling in the unloaded state, thus with a nil angle of torsion. Figures 2 to 5 show different operating stages of the coupling, using one of the sets 23 of springs as an example, and assuming that the position of the hub 21 remains unchanged and the outer ring 22 is twisted increasingly in the clockwise direction. It can be seen that here the flanking springs 31, 32, 33-in this instance these are the so-cailed front flanking springs-rest constantly on the main springs 30 and support them.

In Figure 2 the stop 46 on the outer ring 22 has engaged-at an angle of torsion a-with the longest of the rear flanking springs, which is designated 36, as has the stop 47 in Figure 3-at the greater angle of torsion b-with the spring 37, and in Figure 4 the stop 48-at the still greater angle of torsion c-with the spring 38. In Figure 5 the angle of torsion has finally risen to the value d.

This is the position in which the rear flanking springs 36, 37 and 38 have all come into contact, together with the main spring 30 and now act as an end stop. However, in this case, this is not a rigid end stop since the coupling still has a slight amount of elasticity even in this state. Below the angle of torsion d the springs 36, 37 and 38 act as individual springs, as Figure 4 shows particularly clearly.

Obviously, the transmission of force can also take place in the other circumferential direction, differing from what is shown in Figures 2 to 5. In this case the leaf springs 36, 37, 38 take over the function of the front flanking springs and the leaf springs ,32,33 assume the function of the rear flanking springs.

In connection with Figure 1 it should be mentioned that, in a known way, side discs, which are not shown in the Drawing, can be attached to the outer ring 22. In addition to the bores 28 provided in the radially outer region, further bores 29 are provided, located in the radially inner zone of the outer ring 22, for the bolts required for these side discs.

The side faces of the grooves 27 and the abutment surfaces 41 , 42, 43 and 46, 47, 48 can be fitted with plating reinforcement, as indicated at 19, thereby being protected against wear.

In Figures 6 to 9 a construction example is shown which is modified from that shown in Figures 1 to 5. The hub of this coupling is designated 51 , the outer ring 52 and one of the sets of leaf springs 53, its main springs being designated 60, the front-in the direction of the flow of force shown here-flanking springs being designated 61 and 62 and the rear flanking springs 66 and 67. The flanking springs again have abutment surfaces 71,72, 76, 77 on the outer ring 52 appertaining to them. The distance between the abutment surfaces 71 and 72 or 76 and 77 respectively, measured in the circumferential direction, is greater than in Figures 1 to 5.This means that the following is achieved: After the angle of torsion e (Figure 7), at which the first rear flanking spring 66 comes into contact with its abutment surface 76, has been exceeded, the spring 66 is made to lie on the main springs 60 at the latest by the time the next spring 67 engages with its stop 77. This happens at the greater angle of torsion f (Figure 8). With a further increase in the angle of torsion to the value g (Figure 9), the spring 67 is also brought to rest on the remaining springs of the set. This method could naturally also be applied with a set of springs with a greater number-of flanking springs, i.e. with a more finely graduated set of springs.

The essential point is that as the angle of torsion becomes greater the radius of the application of force becomes increasingly smaller as the flanking springs 66, 67 become engaged, and simultaneously the thickness of the part of the set of springs which is in the block state increases stepwise. This means (see Figure 9) that at the maximum angle of torsion, the stop 77 appertaining to the shortest spring 67 transmits substantially all the circumferential force to the set 53 of springs, while the ends of the remaining springs 66 and 60 are virtually free of force. This can also be seen in Figure 9, in that above the innermost stop 77 the set of springs is no longer bent.

Figure 1 0 shows the path of the characteristic coupling curve K of the coupling 20 shown in Figures 1 to 5. In this diagram the torque M which can be transmitted by the coupling is shown over the angle of torsion W. As already stated in the above explanation of Figures 2 to 5, the torsional rigidity of the coupling increases in each case at the angles of torsion a, b, c and d. This is shown in Figure 10 by the increasingly steeper rise of the characteristic curve. In the same way, Figure 11 shows the characteristic coupling curve K' for the construction example shown in Figures 6 to 9. The steeper overall path of this characteristic curve can be seen clearly.

Figures 1 2 and 1 3 show a further construction example of the invention, where the hub is designated 81, the outer ring 82 and one of the sets of leaf springs 83, while a recess in the outer ring 82 for the set 83 of springs is designated 86.

This is defined by smoothly curved surfaces 87, as opposed to the stepped surfaces of the previously described construction example. The spring ends of the set 83 of leaf springs which engage with these surfaces 87 are rounded. Figure 12 illustrates the rest state of this coupling, while Figure 1 3 shows the state with maximum angle of torsion.

In all the construction examples, the sets of leaf springs and the recesses with the abutment surfaces are symmetrically formed, so that an identical effect is achieved for the coupling in the two directions of the flow of force. However, naturally, asymmetrical shaping of the sets of leaf springs and/or the recessas provided in the outer ring can be provided if required, if the increase in torsional rigidity of the coupling is to be unequal in the two directions of the flow of force.

The special manner in which the sets of leaf springs are attached to the hub with the aid of the wedge-shaped intermediate elements 24 and 25 has already been indicated above. This design affords a considerable simplification compared with the leaf spring coupling known from DE-PS 555 438. In the latter case, each set of leaf springs has a T-shaped foot. One side of this is fitted in an annular recess in the hub and the other side in an annular recess in a covering ring. This method of construction is expensive owing to the said T-shaping of the foot of the leaf springs and because, in addition to the hub, the said covering ring is required. Conversely, in the coupling according to the invention the individual leaf springs can have a simple rectangular shape; they can therefore be produced very much more cheaply, since they can preferably be cut from strip material. In addition, the above-mentioned covering ring is not required.

The attachment of the sets of leaf springs in the hub instead of in the outer ring (corresponding to the coupling known from the Kupplungs-Atlas) has the following advantages: the conical intermediate ring which is necessary for the known coupling is not required, and therefore the forming of the corresponding conical inner surface on the outer ring is also not necessary. If the interior of the coupling is filled with lubricating medium the lubrication of the engagement points of the main springs 30 in the outer ring 22 is still guaranteed when some of the lubricating medium has vanished, since the lubricating medium always comes to rest against the outer ring 22 during operation, due to centrifugal force.

The arrangement of the sets of leaf springs 23 on the hub 21 should be such that the distances between the sets of leaf springs are as uniform as possible. The achieving of this aim is greatly facilitated due to the fact that, as already mentioned, every second intermediate element 24 of the intermediate elements 24 and 25 is integral with the hub 21, and only the remaining intermediate elements 25 are bolted onto the hub 21. This means that the position of the sets 23 of leaf springs in the circumferential direction can be established very exactly without any difficulty.

In order to provide still further increased security against possible release of the sets 23 of leaf springs from the hub 21, the shortest outer leaf springs 33 and 38 can be replaced by discs made of a material which is relatively soft and which therefore dents readily, such as normal unhardened steel, for instance, or provision may be made in other ways for the outer surfaces of these leaf springs 33 and 38 to be formed by an additional layer made of a material which can be dented. At the same time, the edge faces of the intermediate elements 24, 25 which are in contact with these facings are roughened. In this way, good holding of the sets 23 of leaf springs in the hub 21 is ensured, with increased reliability.

For the same purpose, the measures shown in Figure 1 4 can be incorporated. According to this, the outermost leaf springs of a set 93 of leaf springs are replaced by wedges 91; these are component parts of the set of leaf springs, which thereby obtains an approximately dovetail-shaped foot, viewed in the axial direction. The shape of the intermediate elements 94 and 95 is adapted to this foot.

The leaf spring coupling according to the invention can advantageously be arranged in vehicle drives as an elastic coupling and oscillation damper between an internal combustion engine and a load-switching gear.

Claims

1. A leaf spring coupling of the kind having an inner coupling half and an outer coupling half, which are inter-connected rotationally and elastically via radially arranged sets of leaf springs which, in the form of a body with uniform bending stress, have variously long leaf springs, such that the longest leaf springs ("main springs") have a plurality of so-called flanking springs appertaining to them, the length of which decreases stepwise from spring to spring, the sets of leaf springs being clamped in one of the coupling halves and engaging via their main springs in the other coupling half, characterised in that the other coupling half has stops for the transmission of torque which are arranged to engage with at least some of the flanking springs, after a certain angle of torsion has been reached.

2. A leaf spring coupling according to Claim 1, characterised in that such stops are provided only in one of the two circumferential directions.

3. A leaf spring coupling according to Claim 1, characterised in that such stops are provided in both circumferential directions.

4. A leaf spring coupling according to any one of Claims 1 to 3, characterised in that each flanking spring has a stop appertaining to it.

5. A leaf spring coupling according to any one of Claims 1 to 4, characterised by an arrangement of the stops such that the individual flanking springs of each set of leaf springs engage with their stops at different angles of torsion.

6. A leaf spring coupling according to Claim 5, characterised by an arrangement of the stops such that, after becoming engaged with the stops as the angle of torsion increases, the flanking springs act firstly as individual springs, and come to rest against each other and/or against the rest of the set of springs only after further increases in the angle of torsion.

7. A leaf spring coupling according to any one of Claims 1 to 5, characterised by an arrangement of the stops such that a flanking spring engages with its stop at the earliest at that angle of torsion at which the flanking spring which has previously become engaged rests on the rest of the set of springs.

8. A leaf spring coupling according to any one of Claims 1 to 7, characterised in that all the sets of leaf springs are identical with each other.

9. A leaf spring coupling according to any one of Claims 1 to 8, characterised in that, in individual sets of leaf springs or in all the sets of leaf springs, the leaf springs have different plate thicknesses.

10. A leaf spring coupling according to Claim 9, characterised in that in one set of leaf springs the plate thickness increases from leaf spring to leaf spring in such a way that the shorter the leaf spring, the thicker is the plate.

11. A leaf spring coupling according to any one of Claims 1 to 6 or 8 to 10, characterised by an arrangement of the stops associated with a set of springs such that the bending line of the leaf springs is as least approximately the arc of a circle.

12. A leaf spring coupling according to any one of Claims 1 to 10, characterised in that the stops associated with a set of springs is formed by a continuously curved surface on the other half of the coupling and the ends of the leaf springs are rounded.

1 3. A leaf spring coupling according to any one of Claims 1 to 12, characterised in that the sets of leaf springs are clamped in the inner coupling half and engage via their main springs in the outer coupling half.

14. A leaf spring coupling according to Claim 13, with wedge-shaped intermediate elements appertaining to the inner coupling half and arranged between the sets of leaf springs, characterised in that, with the aid of bolts extending approximately in the radial direction, the wedge-shaped intermediate elements are the only fixing means for clamping in the sets of leaf springs at the inner coupling half.

1 5. A leaf spring coupling according to Claim 14, characterised in that only every second one of the wedge-shaped intermediate elements is bolted to the inner coupling half, and the rest-are integral with said inner coupling half.

16. A leaf spring coupling according to Claim 1 4 or 15, characterised in that the intermediate elements have a rough surface on the face which is in contact with the sets of leaf springs, and that the edge surfaces of the sets of leaf springs which are in contact with the intermediate elements are formed by additional layers made of a material which dents readily.

1 7. A leaf spring coupling according to Claim 14 or 15, characterised in that in the individual sets of leaf springs, a wedge is arranged on the outer face of at least one of the two outermost leaf springs so that the thickness of the set of leaf springs increases in the direction of the axis of rotation, the shape of the intermediate elements resting against the wedge being adapted accordingly.

18. A leaf spring coupling according to any one of claims 1 to 17, characterised in that the outer coupling half is made of light-weight metal.

1 9. A leaf spring coupling according to any one of Claims 1 to 5, characterised in that the outer coupling half has reinforcement made of a wearresistant material on the grooves.

20. A leaf spring coupling according to Claim 19, characterised in that the reinforcement also covers the abutment surfaces.

21. A leaf spring coupling constructed, arranged and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.