GB2192969A

GB2192969A - A universal joint for interconnecting shafts

Info

Publication number: GB2192969A
Application number: GB08717106A
Authority: GB
Inventors: John Constantine Grey
Original assignee: Hackforth GmbH and Co KG
Current assignee: Hackforth GmbH and Co KG
Priority date: 1986-07-26
Filing date: 1987-07-20
Publication date: 1988-01-27
Also published as: IT1211656B; FR2602016A1; GB8717106D0; BR8703849A; GB8618282D0; IT8748184A0; FI873194A; CN87105237A; FI873194A0; JPS6334326A; DE3722511A1

Description

GB2192969A 1

SPECIFICATION

A universal joint for interconnecting shafts The invention relates to a universal joint for interconnecting shafts having a metal input disc and 5 a metal output disc interconnected by at least one metal diaphragm ring or stack of diaphragm rings.

Universal joints of this kind require no lubrication or servicing and are being increasingly used in heavy-duty, industrial and marine drives and propulsion systems. Considerations of space often make it necessary for the joint to be of very reduced diameter. However, the torque which 10 has to be transmitted calls for a correspondingly high number of screwed fasteners operative to connect the diaphragm ring to the input disc and output disc. Consequently, the resilient properties of such a joint-Le. its axial resilience and its angular resilience-are greatly restricted and the joint is likely to fail because of premature fatigue.

In universal joints of this kind it is known for the diaphragm ring to be secured alternately to 15 the input disc and output disc by four or six or eight or ten or more screwed fasteners disposed equidistant from one another on a pitch circle, each screwed fastener on the input disc transmitting, by way of the connecting element formed by the diaphragm ring from screwed fastener to screwed fastener, a corresponding proportion of the torque to the adjacent screwed fastener of the output disc. For example, a universal joint having four screwed fasteners has two 20 input screwed fasteners and two output screwed fasteners, a universal joint having six screwed fasteners has three driving and three output screwed fasteners and so on. The axial rigidity of the joint increases very rapidly with the number of screwed fasteners and local stresses in the diaphragm rings at the securing places considerably limit the performance of such a joint.

A conventional way of securing the diaphragm rings to the metal disc by using screwed 25 fasteners is to use circular shims having a rounded annular edge, the aim being to avoid overstressing when the ring is bent as the joint makes angular deflections.

It is the object of the invention to devise a universal joint of the kind hereinbefore set out which can transmit a much higher torque than a known universal joint of the same overall dimensions and which returns resilient properties such as axial and angular resilience. It is 30 another aim of the invention so to devise the universal joint as to obviate overstressing of the diaphragm ring at its securing places.

According to the invention, therefore, starting from a universal joint of the kind hereinbefore described, a flexible coupling of the multiple membrane type comprising a round number of corner fixing bolts disposed on a single circle or adjacent and concentric bolt circles in a manner 35 such that force is transmitted by alternately placed bolts in order to substantially increase the free length of the membranes thereby increasing the axial and angular flexibilities of the coupling without increasing its diameter.

A diaphragm ring devised as a number of elements in the peripheral direction can be used instead of a unitary diaphragm ring. 40 The main advantage provided by the invention is that the use of two parallel-connected diaphragm rings enables virtually twice the torque to be transmitted which can be handled by a joint having a single diaphragm ring, without any loss of resilience. This is achieved mainly because the diaphragm rings are "necked" in order to achieve a superimpositioning of two diaphragm rings with 2 n screwed fasteners, so that a universal joint of this kind can handle a 45 torque associated With 2 n screwed fasteners with the resilience of a diaphragm ring having just n screwed fastener.

Advantageously, to avoid overstressing in the clamping zones, metal support plates are dis posed at such zones on both sides of the diaphragm rings. Preferably, the support plates can be flexibly resilient. 50 The support plates support the diaphragm rings in the clamping zones and prevent overnarrow bending radii such qs may occur on the rounded edges of shims.

Embodiments of the invention will be described in greater detail hereinafter and are diagram matically illustrated in the drawings wherein:

Figures 1 to 3 are plan views of three known diaphragm rings showing the passages for the 55 screwed fasteners, the clamping discs and the corresponding span of the connection on which its resilience depends, Figure 4 is a plan view of two diaphragm rings disposed one above another in accordance with the invention and each formed with four passages for screwed fasteners, Figure 5 is a side view of a convex diaphragm ring, 60 Figure 6 is a plan view of a universal joint having eight screwed fasteners according to the invention, Figure 7,7a comprises a number of partial views, partly in section, of a clamping zone of a diaphragm ring according to the invention, and Figure 8 and 9,9p comprise partial views of a clamping zone of a conventional diaphgram ring. 65 2 GB2192969A 2 Referring to Fig. 1, membrane 1 represents a typical 4-bolt form with 2 driving bolts 2 and 3 and 2 driven bolts 4 and 5. The clamping washers 6 allow a free flexing length L1 in the link from bolt 2 to bolt 5.

Fig. 2 shows a 6-bolt membrane with 3 driving bolts 7, 8 and 9 and 3 driven bolts 10, 11 and 12, with a free flexing length of L2. 5 Fig. 8 shows a 8-bolt membrane with 4 driving bolts 13, 14, 15 and 16 and 4 driven bolts, 17, 18, 19 and 20 with a free flexing length L3 Fig. 4 shows a 8-hole duplex system of 4-bolt membranes according to the invention. The 4 driving bolts, 21, 22, 23 and 24 are shown to be adjacent in pairs, as are the driven bolts, 25, 26, 27 and 28. Note the free flexing length is L1 as in Fig. 1, with L1 g 2.5 x L3 It is shown 10 in the analysis below that a relative axial displacement between the driving and driven bolts induces a tensile stress in the links and an axial force reaction, as follows:

In a 8-bolt coupling as in Fig. 3 the axial reaction is about 15 times greater than in a 8-bolt coupling as in Fig. 4. Similarly, the corresponding tensile stress will be about 6 times greater than in Fig. 4. 15 Fig. 5 shows two adjacent membrane links 29 with their associated clamping washers 30, 31 and 32. The membrane is diagrammatically shown deflected as in 33, with the free span L extended as shown.

20 F- --,E 4c:t- eC-- 6 25 where F = axial thrust resulting from two adjacent links S = tensile stress induced in the links y = axial deflection of the membrane L = free length of 1 link a = cross sectional area of 1 link 30 E = elastic Modulus of the membrane material The expressions above indicate that the axial stiffness of the coupling is inversely proportional to the c be of the free length link and the stress induced is inversely proportional to the square of the free length. This explains the claim made above, of the advantages of the configuration in 35 Fig. 4 over that of Fig. 3. Similar considerations apply to couplings of higher orders viz. 10, 12 etc. bolt types.

Fig. 6 shows, by way of example, a typical construction of a 8-bolt coupling incorporating the principle illustrated in Fig. 4. Two identical rigid rings 34 and 35 support the duplex arrangement of membranes. Bolts 36, 37, 38 and 39 attach the driving corners of the two membrane stacks 40 to the driving coupling half ring 34 and bolts 40, 41, 42 and 43 attach the driven corners of the two membrane stacks to the driven coupling half 35. It is convenient to use a number of smaller threaded holes, 44 to fix the driving ring to the driving shaft hub and the corresponding holes 45 on the driven ring 35, to the coupling spacer and thence to the driven shaft via a second flexible coupling identical to the one in Fig. 6. 45 Figs. 8 and 9 describe the disadvantages of the current methods of bolting the flexing membranes to the rigid hubs and Fig. 7 describes the solution offered in this invention.

Fig. 8 shows a membrane stack 46 bolted to a rigid flange 47, deflected as shown in Fig. 5 and clamped by twq washers 48 and 49 having sharp edges at A. The tensile force T in the 50. link arises (a) from the torque transmitted by the coupling and (b) from the deflection illustrated 50 by Fig. 5. The stress at point A is the sum of three additive stresses:

(a) tensile stress due to force T.

(b) bending stress at A due to force T (c) stress concentration at A due to the nature of the contact at A between the washer 49 and the membrane in contact with it. 55 Fig. 9 shows the current method of reducing the bending stress (b) and (c) above. The clamping washers 50 and 51 have a radiused edge at B of curvature p resulting in a toroidal surface C extending from diameter D1 to D2. This method has the following disadvantages:

(a) Any attempt to increase the radius p so as to reduce the bending stress in the membrane, simultaneously reduces the diameter D1 and thence compromises the proper clamping of the 60 membrane.

(b) In the deflected state, the membrane tends to bend about an axis X-X at right angles to the tensile force T. The support contact at D between the washer 50 and the membrane is in the plane Y-Y at right angles to X-X, leaving the portions 'a' and V of the bent membrane totally without support and introducing a further complex stress pattern at D, both dependent on the 65 3 GB2192969A 3 tensile force T.

Fig. 7 shows a cantilever support according to the invention not subject to the drawbacks described above. The membrane stack 52 is shown clamped between two circular washers 53 and 54 and two additional supports 55 and 56 having the approximate outline of the corners of the membrane. In a bent plate of rectangular section the relationship between stress and 5 curvature is as follows:

10 where s = bending stress.

t = thickness of plate 15 p = curvature due to bending E = elastic modulus. of material.

The following features are essential to the design of these plates.

(a) The proportions of the plate i.e. the thickness t and its overhang length 1 may be chosen to maximise the radius of curvature p thereby reducing the curvature and stress of the membrane 20 " by compelling it to follow the curvature of the plate.

(b) The plate and the adjacent membranes bend about an,axis X-X thus avoiding the stress concentration at D of Fig. 9.

(c) A reasonable length 1 of the plate may be used to optimise the curvature p and this is particularly possible with the substantial link length L1 shown;n Fig. 4. 25 (d) The plates 55 and 56 are only subjected to the bending imposed by the membranes and are independent of the tensile force T which affects the aggregate stress of the membrane links.

(d) The plates do not contribute and are not affected by the torque transmitted by the coupling.

They may be made of a different material than is normally used for the membranes and therefore hardened and tempered to sustain bending stresses in excess of what is normally 30 prescribed for the membranes.

(f) The plates described preferally function as elastic members i.e. are normally plane in their free state. Alternatively they may be manufactured pre-formed as shown by plate 55.

Claims

CLAIMS 35

1. A flexible coupling of the multiple membrane type comprising around number of corner fixing bolts disposed on a single circle or adjacent and concentric bolt circles in a manner such that force is transmitted by alternately placed bolts in order to substantially increase the free length of the membranes thereby increasing the axial and angular flexibilities of the coupling without increasing its diameter. 40

2. A flexible coupling as claimed in Claim 1 wherein the flexible membranes are replaced by separate flexible links.

3. A flexible coupling as claimed in Claim 1 wherein elastic support plates are clamped between the corner washers and the membranes to increase the curvature of the membranes during the cyclic flexing when in misalignment. 45

4. A flexible coupling as claimed in Claim 1 wherein rigid support plates are clamped between the corner washers and the membranes to increase the curvature of the membranes during the cyclic flexing when ip misalignment.

5. A flexible coupling substantially as described herein with reference to Figures 1 to

6 of the accompanying drawipgs. 50 6. A universal joint for interconnecting shafts having a metal input disc and a metal output disc interconnected y at least one metal diaphragm ring or stack of metal diaphragm rings, the diaphragm ring being connected both to the input disc, by way of a first group of screwed fasteners distributed, uniformly in pairs over the periphery, and also to the output disc, by way of a second group of screwed fasteners distributed uniformly in pairs over the periphery and 55 nested in the peripheral direction with the fasteners of the first group, characterised in that the input disc and output disc are interconnected by at least two parallel- connected diaphragm rings which are disposed in a peripheral position offset from one another by half the pitch or less between adjacent screwed fasteners of a group, the fasteners of both rings are disposed on a single pitch circle or on adjacent concentric pitch circles, and the diaphragm rings are formed on 60 their periphery between two consecutive fasteners with a necking of a depth such that the peripheral edge extends on the radially inwards side of the fastener of the other diaphragm ring.

7. A joint according to Claim 6, characterised in that each diaphragm ring comprises a number of elements in the peripheral direction.

8. A joint according to Claim 7, characterised in that each diaphragm ring is embodied by a 65 4 GB2192969A 4 number of identical elements corresponding to the number of the associated screwed fasteners.

9. A joint according to any one of claims 6 to 8, characterised in that metal support plates are disposed on the clamping zones of the diaphragm rings-i.e. on the screwed fasteners-on both sides of such rings. 5

10. A joint according to Claim 9, characterised in that the support plates are resiliently flexible. 5

11. A universal joint for interconnecting shafts having an input disc and an output disc interconnected by, at least two parallel-connected generally annular diaphragms, the diaphragms being connected both to the input disc, by way of a first group of fasteners distributed uniformly in pairs around their periphery and also to the output disc, by way of a second group of fasteners distributed uniformly in pairs around their periphery and disposed intermediate pairs 10 of fasteners of the first group, the diaphragms being offset from one another by half the pitch or less between adjacent fasteners of a group, the fasteners being disposed on a single pitch circle or on adjacent concentric pitch circles, and the diaphragms are formed on their peripheries between two consecutive fasteners connected to the respective diaphragms with a necking or indentation of a depth such that the peripheral edge extends on the radially inwards side of the 15 intermediate fastener on the other diaphragm.

Published 1988 at The Patent Office, State House, 66/71 High Holborn London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RE Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.