GB1593089A - Overload couplings - Google Patents

Description

PATENT SPECIFICATION

OC ( 21) Application No 6229/80 ( 22) Filed 31 October 1977 ( 62) Divided out of No 1 593 088 ( 31) Convention Application Nos 7612079 7701013 7701012 c ( 32) Filed 1 November 1976 1 February 1977 1 February 1977 in V) ( 33) Netherlands (NL) r ( 44) Complete Specification published 15 July 1981 ( 51) INT CL 3 F 16 D 9/00 ( 52) Indexat Acceptance F 2 X 2 OVERLOAD COUPLINGS ( 71) We, C VAN DER LELY N V, of 10, Weverskade, Maasland, The Netherlands, a Dutch Limited Liability Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: -

This invention relates to overload couplings.

According to the present invention there is provided an overload coupling suitable for us in a rotary drive mechanism, the coupling comprising two members which are rotatable about a common axis, and at least one frangible element, which is disposed at least partly in a holder connected for rotation with one of the members, the frangible element being capable of co-operating, in normal operation when in a connecting position, with the other member to interconnect the members for rotation together in at least one direction, the members being relatively rotatable subsequent to fracture of the frangible element upon overload of the coupling, until the same or another frangible element takes up a connecting position in which the interconnection of the members is reestablished, at least part of the holder being releasably connected to the said one member by a quick-release connection.

The present invention also provides a shaft having at least one universal joint and at least one overload coupling as just defined.

Embodiments of the present invention provide overload couplings which match the desired efficiency of the use of modern machinery and are particularly suitable for use in machine locations to which access is difficult for replacing a fractured frangible element, for example in large agricultural machines.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Figure 1 is an elevational view partly in cross-section of a first embodiment of an overload coupling; Figure 2 is an elevational view taken in the direction of the arrow II in Figure 1; Figure 3 is an elevational view of part of a ( 11) 1 593 089 second embodiment of an overload coupling; Figure 4 is a sectional view taken on the line IV IV in Figure 3; Figure 5 is a sectional view taken on the line V-V in Figure 3; 55 Figure 6 is an elevational view partly in cross-section of a third embodiment of an overload coupling; Figure 7 is an elevational view taken in the direction of the arrow VII in Figure 6; 60 Figure 8 shows an alternative construction for part of the coupling of Figure 6; Figure 9 is a sectional view taken on the IX-IX in Figure 8; Figure 10 is an elevational view of a fourth 65 embodiment of an overload coupling; Figure 11 is an elevational view taken in the direction of the arrow XI in Figure 10; and Figure 12 is a sectional view taken on the line XII-XII in Figure 11; 70 Figure 13 is a sectional view of a fifth embodiment of an overload coupling; Figure 14 is an elevational view taken in the direction of the arrow XIV in Figure 13; Figure 15 is a sectional view taken on the 75 line XV XV in Figure 14; Figure 16 is an elevational view taken on the line XVI XVI in Figure 13; Figure 17 shows separately a component suitable for use in the coupling of Figures 13 to 80 16; Figure 18 shows an alternative construction for part of the overload coupling of Figure 13; Figure 19 is a sectional view of a sixth embodiment of an overload coupling; 85 Figure 20 is a sectional view taken on the line XX XX in Figure 19; Figure 21 is an elevational view of part of the coupling of Figure 19; Figure 22 is a sectional view taken on the 90 line XXII XXII in Figure 21; Figure 23 is a sectional view of part of a seventh embodiment of an overload coupling; and Figure 24 is a sectional view taken on the 95 line XXIV XXIV in Figure 23.

The overload coupling shown in Figure 1 comprises a coupling member 1, which is connected in this embodiment in a manner not shown with a universal shaft The coupling 100 1 593 089 member 1 comprises a hollow shaft 2 which is rigidly connected near one end to a coupling plate 3 extending for some distance in a radial direction The plate 3 extends outwardly in the shape of a tag, as shown in the elevational view of Figure 2, and near its end remote from the shaft 2 it has a width substantially corresponding to one third of the diameter of the shaft 2 To the end of the coupling plate 3 remote from the shaft 2 is welded a ring 4 extending axially of the shaft 2 away from the plate 3.

The shaft 2 is rotatable about a rotary axis 2 A.

The face of the ring 4 remote from the rotary axis is provided with a connecting arrangement comprising a holder 5 containing a frangible connecting element 7 The holder 5 extends away from the ring 4 in a radial direction to the side away from the axis 2 A The holder 5 comprises a cylindrical sleeve The frangible element 7 comprises a shear pin having a plurality of weakened, breakable zones The outermost end of the shear pin 7 is received in an annular seat 8 having, at the side remote from the shear pin, an abutment surface for a helical compression spring 9 extending from the seat 8 to near the outermost end of the holder 5 The outermost end of the spring 9 engages a circular plate 10, which abuts a guide pin 11 to restrain the spring in a radial direction The guard pin 11 has a locking ring 12 so that the pin 11 can be fixed in place on the holder 5.

Inside the ring 4 is fitted a sleeve 13 which extends away from the holder 5 towards the rotary axis 2 A and serves to absorb torque transferred by the shear pin 7 To this end, the sleeve 13 is in intimate engagement with the shear pin 7 The sleeve 13 may be made from hardened material.

The shear pin 7 normally connects the coupling member 1 with another coupling member 14 The coupling member 14 comprises a coupling plate 15 located coaxially with the rotary axis 2 A and extending over some distance in an axial direction It has near the rotary axis 2 A a cylindrical opening.

The coupling plate 15 is provided with a sleeve 16 for receiving one end of the shear pin The sleeve 16 is preferably made from hardened material and is arranged replaceably in the coupling plate 15 The sleeve 16 has an opening 17 for receiving the end of the shear pin, this opening being cylindrical in this embodiment and having a diameter slightly exceeding the diameter of the shear pin 7 The wall of the opening 17 is parallel to a cylindrical surface the axis of which extends radially of the rotary axis 2 A, but may as an alternative be parallel to a conical surface the vertex of which lies on the rotary axis 2 A The opening 17 extends radially for about one quarter of the radial length of the sleeve 16 The opening 17 is blind and its bottom is at the radially inner end for co-operation with the end of the shear pin 7 The coupling member 14 comprises a shaft portion 18 which is rigidly connected with the coupling plate 15 and is fastened in the cylindrical opening in the coupling plate 15.

The shaft portion 18 extends inwardly from the coupling plate 15 for some distance towards the rotary axis 2 A The shaft portion 18, as 70 shown in the elevational view of Figure 2, is provided with serrations 19 for transferring a high torque to a shaft (not shown) coupled to the shaft portion 18 Inside the shaft portion 18 is received in a sleeve 20, which is pressed 75 into the shaft 2, the material of this sleeve 20 being appropriate to the intermittent function of the sleeve 20 as a sliding bearing for the shaft portion 18 The sleeve 20 and the shaft portion 18 are fixed against an axial displacement by a 80 key formed by a bolt 21 which is held in place by a nut The sleeve 20 and the shaft portion 18 have for this purpose corresponding annula openings 22 which are coaxial with the rotary axis 2 A 85 In operation the overload coupling shown in Figures 1 and 2 may be employed between two shaft portions or between a shaft and machine components, for example, components of an agricultural machine, for protecting the 90 machine components and the shafts against overloading For this purpose the shear pin 7 is adapted to transmit a predetermined maximum torque is exceeded, the portion of the shear pin 7 engaging the wall of the opening 95 17, which acts as an abutment, will break off.

After this portion of the pin has broken off, the coupling members rotate about the rotary axis 2 A relatively to each other although they are still axially fixed together by the bolts 21 100 When the connection between the two coupling members is broken, the driving coupling member will continue to rotate, but the driven coupling member will very soon or after a short time come to a standstill in dependence upon 105 the magnitude of the overload Since the coupling member 1 continues to rotate, the holder 5 and the associated shear pin 7 also continue to rotate As a result, centrifugal force will bias the shear pin outwardly against the 110 pressure of the spring 9 The characteristic of the spring 9 is preferably adapted to the inertia of the shear pin Owing to the balance between the centifugal force acting on the mass of the shear pin 7 and the force of the spring 9, the 115 shear pin 7 will be urged with only very slight pressure against the supporting surface formed by the radially outer wall of the plate 15 and towards the opening 17 during the continued rotation of the coupling member 1 Thus under 120 these conditions the shear pin 7 is not capable of re-establishing the connection between the coupling members The connection between the two coupling members will not be established until the speed of rotation of the 125 coupling member 1 has been appreciably reduced by uncoupling the drive, when the spring 9 will act as advancement means for advancing the pin 7 into re-engagement with the opening 17 This can be achieved by 130 1 593 089 matching the circumferential extent of the opening 17 to the diameter of the pin 7, the intertia force of the pin, and the characteristic of the spring 9 The circumferencial extent of the opening 17 is a function of the factor T in the formsla S = A T 2, in which S is the distance to be covered by the pin towards the bottom of the opening 17 in order to reestablish a connection between the two coupling members The factor A is a function of the force of the spring 9 and the mass of the pin 7.

In order to keep the factor A constant however many times the pin 7 has been fractured, the reduction of the spring force due to the radial inward shift of the pin 7 after fracture should be proportional to the reduced mass of the pin.

The circumferential extent of the opening 17 is preferably about twice the diameter of the shear pin The speed at which the pin 7 re-establishes the connection is preferably chosen to be lower than the minimum possible self-sustaining speed of the driving engine In this way the pin cannot prematurely reestablish the connection while the engine is still running at a speed reduced by the overload and while the drive is still in engagement.

It should be noted that since the opening 17 extends radially, the broken-off fragment of the shaver pin 7 is automatically thrown out of the opening 17, and a further portion of the shear pin 7 automatically re-establishes the connection once the speed is reduced The opening 17 thus acts as release means or as an ejector for the broken-off fragment Since, after overload, the operator can re-establish the connection between the two coupling members only when he has intentionally reduced the driving speed by an appreciable amount, inadvertent continuous repeated fracture of the pin will be avoided.

Such a shear pin coupling is particularly advantageous in agricultural machines, especially between parts to which access is difficult or inconvenient or to which access is not possible at all during operation When the shear pin, which preferably has at least five breakable portions and may advantageously comprise ten portions, has been completely used up by repeated overloads, it can be removed in a very simple manner It is only necessary to remove the guard pin 11 and to slip a new shear pin 7 into the holder 5 The shear pin can have so many breakable portions that it may be necessary to replace it only at normal periodical inspection or servicing of the machine.

Figures 3, 4 and 5 show a second embodiment of an overload coupling comprising a coupling member 23 formed by a hollow shaft portion 24 rotatable about a rotary axis 24 A and having key ways 25 on its inner side for receiving a driving stub shaft (not shown).

The shaft portion 24 is provided near one end with a coupling flange or plate 26 which is coaxial with the shaft portion 24 The edge of the plate 26 remote from the shaft portion is provided near the circumference with an annular supporting member 27, comprising 70 a fastening portion 28 extending inwardly from the outer circumference of the coupling plate 26 The fastening portion 28 is fixed in place of means of equispaced bolts 29 near the circumference of the coupling plate 26 The 75 fastening portion 28 has tapped holes for receiving the bolts 29 The free end of each bolt is not screw-threaded and forms a stub shaft 30 so that the bolts can each serve in addition as a pivot pin for a torsion spring 31 80 looped over the stub shaft 30 The action of this spring 31 is comparable with that of the spring 9 of the preceding embodiment The supporting member 27 furthermore comprises a supporting part 32 which is perpendicular to 85 the portion 28 and which is coaxial with the rotary axis 24 A The supporting part 32 has radial recesses 33 for supporting and guiding shear pins 34 each having, in this embodiment, seven portions 35 The longitudinal centre lines 90 of the pins 34 extend substantially radially The shear pin portions 35 are separated one from another by locally weakened transitional zones 36 The thickness of the supporting part 32, in a radial direction, is preferably such that 95 approximately two shear pin portions 35 are accommodated in the recess 33 at any one time The diameter of the recess 33 is such that it closely surrounds the shear pin 34, but allows movement in a radial direction Each 100 torsion spring 31 has a free end which bears on the outermost end 35 of the respective shear pin 34 One limb of the spring bears on the shear pin 34, whereas the other limb, which is inclined to the first limb, passes through an 105 opening 37 in the fastening portion 28 A bent over part of this limb is received in an annular groove 38 in the side of the outer edge of the coupling plate 26 facing the supporting member 27 (Figure 4) The spring 31, using the bolt end 110 as a fulcrum pushes the shear pin 34 towards the rotary axis 24 A The supporting member 27 is provided at equal intervals with eight similarly arranged shear pins 34 Seven of these pins are spare and only one is operative at any 115 one time The operative pin 34 connects the coupling member 23 with an associated coupling member 39 The coupling member 39 comprises a flange or coupling plate 40 and a shaft portion 41, whose centre line coincides 120 with the rotary axis 24 A The shaft portion 41 has internal key ways 25 for receiving a driven shaft (not shown).

It should be noted that the two coupling members 23 and 39 are restrained against 125 relative axial displacement by guard means (not shown), as in the preceding embodiment In order to allow thermal expansion, it is desirable to use guard means which allow a small axial displacement of the members 130 1 593 089 The flange 40 has an opening 42 for receiving an end of the shear pin 34 interconnecting the coupling members The opening 42 is bounded partly by a supporting member constituted by a hard metal insert or disc 43 extending radially inwardly away from the circumference of the flange 40 The centre line of the insert 43 is preferably parallel to the centre line of the respective shear pin The io insert 43 has an abutment for the shear pin 34, constituted by a recess surrounding the opening 42 over an arc of about 1000 The opening 42, whose depth approximately corresponds to the height of one shear pin portion 35 and whose radially inner end is blind has furthermore an ejecting or release means formed by a channel 44 for thrusting the broken fragment of the shear pin from the opening The channel 44 has a wall 45, which is curved The wall subtends an angle of about 90 and extends, near the insert, parallel to the centre line of the pin 34, whereas, away from the insert, it is at an angle to the centre line The wall extends to the side of the coupling member 39 remote from the coupling member 23.

During operation the coupling shown in Figures 3 to 5 establishes the connection between a driving part and a driven part of a shaft and/or machine part and it rotates in the direction of the arrow A (Figure 3) The operative shear pin 34 co-operating with the opening 42 is supported in the supporting member 27, which is made of hardened material either wholly or only partly in the region of the supporting part 32 The wall of the opening 42 is furthermore protected by the insert 43 of hard material against undesired deformation In the event of overload the portion 35 located in the opening 42 will break off and this portion will snap from the opening into the channel 44 to be ejected in an axial direction owing to the specific shape of the wall 45 This direction of ejection may be advantageous when the coupling is used with its axis 24 A extending upwards As in the first embodiment, upon fracture of the portion 35 in the opening 42, the two coupling members will rotate relatively to one another, and, due to the overload, the coupling member 39 will come to a standstill either immediately or very quickly, whereas the coupling member 23 maintains the operational speed The torsion springs 31 acting on the shear pins 34 have the same effect as described for the compression spring 9 of the first embodiment In this embodiment, owing to the use of a plurality of equispaced shear pins 34, the coupling as a whole is balanced The coupling can be employed for a very long time without the need to replace the shear pins The construction and disposition of the springs 31 means that the coupling can have a relatively small diameter.

Once the speed of rotation of the coupling member 23 has been reduced, as in the first embodiment, the next-following portion, or a portion of one of the other pins, will reestablish the connection between the coupling members Owing to the number of shear pins the pins will be used at random, and the tendency will be for all the shear pins to be 70 gradually consumed uniformly, without any one pin being used significantly more often than the others It should be noted that the locally weakened transitional zones in the shear pins 34 may also be used in the shear pin 7 of 75 the first embodiment.

In the embodiment shown in Figures 6 and 7, a coupling member 46 is connected, in normal operation, by means of a shear pin arrangement 47 with a coupling member 48 80 The coupling member 46 comprises a shaft portion 49 connected with a radially extending coupling flange or plate 50 The axial end surface of the plate 50 remote from the shaft portion 49 engages a flange or plate 85 51 of the coupling member 48 The plate 51 is provided in the manner described with reference to Figures 1 and 2 with an inner shaft portion 52 intended to receive non-rotabably a shaft by means of axial key ways 53, whilst a 90 key member is provided to prevent an axial movement of the two members, this key member being located in an annular opening in the shaft portion 52 and a surrounding sleeve 54, and being constituted by a bolt 55 95 The shear pin arrangement 47 extends parallel to the rotary axis 49 A of the coupling.

The shear pin arrangement 47 is located in an axially extending holder 56 which is similar to the holder 5 of the Figure 1 embodiment so as 100 to form a housing for a retaining pin 57, a compression spring 58 and a shear pin 59 The shear pin 59 comprises locally weakened zones and is guided in a recess 60 in the plate 51, this recess being preferably provided in a sleeve 61 105 of hard material The operative portion of the shear pin 59 is located in a blind opening 62 to limit the travel of the shear pin This opening has ejecting or releasing means constituted by a channel 63 extending radially outwardly from 110 the opening The channel 63 may have a cylindrical or parallel-sided cross-section, but it may advantageously flare outwardly at its radially outer end, as illustrated The opening 62 may be bounded at least partly by an insert 115 of hardened material in a manner not shown.

Figure 7 shows that four equispaced shear pin arrangements 47 are provided Three shear pins 59 are spare and only one is operative at any one time However, perhaps when a higher 120 torque is to be transmitted, it may be advantageous to have more shear pins in the operative state simultaneously.

In operation the coupling shown in Figures 6 and 7 constitutes an overload safety device as in 125 the preceding embodiments In the event of overload the portion of shear pin located in the opening 62 will break off and it will be effectively and reliably ejected immediately in a radial direction After fracture one of the shear 130 1 593 089 pins 59 can independently restore the connection between the two coupling members.

Also this coupling can be used for a very long time without needing to fit new shear pins.

With the axial disposition of the pins 59 the coupling has only a small diameter.

Figures 8 and 9 show an alternative form of opening and the associated ejecting means suitable for use in the construction shown in Figure 6 An abutment member formed by a rotatable circular disc 64 is received in the coupling plate 50 and can be set in any one of a plurality of positions with the aid of a bolt having a countersunk head, a nut 66 and a dished plate spring 67 The periphery of the disc 64 has semi-circular recesses 68 opening out on the outer side of the disc Four recesses 68 are provided in the disc although other numbers of recesses of could be provided.

Depending on the diameter of the disc and the size of the recesses 68 more recesses, for example, six may be provided One of the recesses 68 opens into an ejecting channel 69 extending rearwardly and outwardly away from the disc 64 with respect to the direction of rotation A of the coupling The longitudinal centre line of this channel 69 is at an angle of about 500 to a radial line going through the recess 68 By turning of the disc, another recess 68 can be positioned to open into the channel 69 In this way the coupling member 46 is safeguarded against damage in the region near the opening 62 in the event of overload.

The direction of the channel 69 with respect to the direction of rotation of the coupling is such that the release and ejection of the broken-off fragment of the shear pin 59 is satisfactorily carried out In the event of damage of recess 68 a new recess 68 can be set and fixed by means of the nut 66 and bolt 65.

Figures 10 to 12 show a fourth embodiment of an overload coupling This coupling comprises, as in the preceding embodiments, a coupling member 70 (Figure 10) formed by a hollow shaft portion 71 and a coupling plate or flange 72 The coupling furthermore comprises a coupling member 73 having a coupling plate 74 The coupling plate 74 extends radially of the rotary axis 71 A of the coupling and is provided near part of its outer edge with a fastening part 75 extending axially for some distance away from the coupling member 70.

Viewed in a direction parallel to the rotary axis 71 A, this part 75 coincides at its outer circumference with part of the circumference of the coupling plate 74 In the embodiment shown the ends of the fastening part 75 subtend an angle of about 800 at the centre of the plate 74 The fastening part 75 comprises furthermore two supporting parts 76 extending radially inwardly towards the rotary axis 71 A.

In the niche bounded by the supporting parts 76 and the fastening part 75 is secured a shear pin unit 77, which comprises an arcuate holder or cassette 78, which can be fastened to the fastening part 75 by means of a quick-release connector 79 The quick-release connector 79 comprises a torsion spring 80 operating to depress a retaining member The holder 78 accommodates in the embodiment shown five 70 shear pins 81 each extending parallel to the axis 71 A Each shear pin 81 is received in a hole of the holder and this hole has a narrow portion 82 adjacent the coupling member 73 This portion 82 serves as a stop for a shoulder 83 at 75 the end of the shear pin 81 remote from the coupling member 73 The top side of the shoulder 83 is engaged by one end of a helical compression spring 84, the other end of which engages a ring 85 and a retaining pin 86 Each 80 of the shear pins 81 passes into a respective aperture 87 serving as a passage Near the lower end remote from the shouldering 83 one of the shear pins is located in an opening 88 similar to the opening 62 in Figure 6 This opening 85 88 has an ejecting channel 89 extending radially outwardly from the opening 88 The coupling plate 74 has furthermore two tapped holes for receiving fastening means of a balancing unit (not shown) for balancing the mass of the 90 holder 78.

In operation the coupling shown in Figures to 12 constitutes an overload safety unit as in the preceding embodiments The shear pins are independently displaceable in the holder 95 78, whilst the holder with the springs 84 operates as advancement means or pressure means for the pins 81 The pins may each be composed of several breakable portions, but the breaking pins 81 may, as an alternative, each 100 have only one breakable portion so that they can be fractured only once In this case the pins 81 together form the breaking pin unit 77 which can re-establish the connection between the coupling members 70 and 73 several times 105 The construction in this embodiment has a great advantage in that the shear pins are located in a holder or cassette 78, which can be readily replaced after fracture of the pins by a fresh holder, with new pins In a preferred 110 embodiment the coupling plate 74 is provided with two diametrically opposite cassettes so that the coupling is balanced As an alternative, only one cassette may be used, in which case separate balancing weights may be pro 115 vided The cassette 78 may be used with great advantage in cases where it may be desirable to exchange the shear pins for ones of a different type to suit a different application.

It should be noted that structural details 120 of the various described embodiments of the couplings may be combined; for example, the opening 42 and the associated ejecting channel 44 of Figure 3 may be employed in the construction illustrated in Figures 10 to 12 This 125 also applied to the use of hardened material around the whole or part of the opening with which the breaking pin portions are cooperating It is furthermore possible to use balancing means of the kind used in the 130 1 593 089 embodiment of Figures 10 to 12 also in the preceding embodiments.

It should be noted that the positions of the coupling members in these embodiments with respect to the driving shaft and the driven shaft may be inverted, i e drive may be transmitted in the opposite direction to that described.

In the embodiment shown in Figures 13 to 17 the overload coupling is substantially symmetrical to a plane of symmetry going through the centre line 90 of the coupling The coupling comprises a coupling member 92 connected with fork parts 91 of a universal coupling and a coupling member 93 co-operating with the member 92 and being connectable with the stub shaft 18 The coupling member 93 comprises a hub 94 having a radial bore 95 holdinga ball 96, which, in normal operation, lies in an annular groove of the stub shaft 18 and is fixed in place in a radial direction with the aid of a retaining bolt 96 A The coupling member 93 comprises furthermore a radially extending flange 98, which is rigidly secured to the hub 94 The coupling member 92 comprises a carrier 99, which is substantially concentric with the hub 94, on which it is journalled by means of a needle bearing 100 The carrier 99 is locked in place axially with respect to the hub 94 by a pressure ring 101 and a retaining ring 102 Four bolts 103 establish a connection between the fork parts 91, the carrier 99 and a circular cutting ring 104, which is at least partly in contact with the flange 98 The cutting ring 104 has a centering plate 105 having a portion 106 bent over at right angles and extending towards the coupling member 93 The bolts 103 secure to the carrier 99 a second centering plate 107 with a portion 108 bent over at right angles extending towards the coupling member 93 The bent-over portions 106 and 108 form retaining rims which retain in place two holders 109, each of which accommodates a plurality of shear pins 110 On the side of the universal coupling, the holders 109 have an edge 111, which can be clamped beneath the portion 108.

The shear pins 110 are each urged by a respective compression spring 112 towards the flange 98 In order to guide the shear pins 110 the holder is provided with sleeves 113, whilst the cutting ring 104 and the centering plate 105 have recesses closely fitting around the shear pins 110 Each spring 112 has, where it engages its pin 110 a number of turns of smaller diameter than the rest of the spring The shear pins 110 and the springs 112 constitute together couplings means with an axial dimension corresponding substantially to the fastening portion of the stub shaft 18.

The flange 98 has an opening 114 having a substantially radially extending channel 115 opening at the outer circumference of the flange 98 The circumferential width of the opening 114 is about 10 to 20 mm depending upon the diameter of the shear pin With respect to the possibility of establishing the connection of the two coupling portions only at a reduced speed, the distance between the shear pin 110 in the opening 114 and the wall of the opening 114 opposite the pin in this embodiment is about 50 to 70 % of the 70 diameter of the shear pin The pin is supported in an axial direction by a bottom part 116 At the side of the opening 114 there is provided a substantially circular cutting plate 117 of hardened material like the ring 104 having a 75 diameter of about 20 to 30 mms The function of this cutting plate is comparable with that of the cutting plate or disc 64 in Figure 8 It has three openings 118 at its circumference and by means of a locating pin 119 the cutting plate 80 can be fixed in place The shear pins can be fixed in the manner shown in Figure 17 in the holder 109 by means of a locking member formed by a common retaining pin 120 When the holder is put in place, the retaining pin 120 85 can be removed from the holder, after which the pins move into their positions Owing to the provision of the centering plate 105 the pins slide, after the removal of the guard pin 120, without further manipulation, into the recesses 90 in the cutting ring 104 By the quick-release connectors formed by the retaining rims 106 and 108 the holders are simply locked in place and the sleeves 113 prevent the shear pins from tipping over If during operation by overload a 95 portion of the connecting shear pin 110 breaks off, the fragment is rapidly conducted away through the channel 115 The width of the opening 114 is such that a shear pin 110 can slip into the opening 114 only after a reduction 100 of the speed of the stub shaft 18 This applies also to the preceding embodiments As in the embodiment shown in Figures 8 and 9, the cutting plate can be set in a different position, should an opening 118 be damaged The 105 coupling can be adjusted in a simple manner to transmit higher or lower powers by providing the holders 109 with matching breaking pins of different strength and by replacing the cutting ring 104 and the centering plate 105 by 110 other ones having matching apertures It should be noted that, as in the case of the holder 78 of Figure 12, the holders 109 can also operate primarily as pressure units for the pins 110.

The variant shown in Figure 18 comprises 115 a holder differing from the foregoing structure.

This holder 121 is closed on top by means of a cap 122 The holder 121 is preferably made from synthetic resin The cap 122 has a cavity for accommodating the end portion of a corm 120 pression spring 123, the other end of which is located in a cavity in a pressure pin 124 The pressure pin 124 presses the shear pin 110 home The pressure pin 124 has a shoulder 125 in sliding engagement with the inner wall of the 125 holder 121 The pressure can thus be manufactured at low cost without detracting from its effectiveness.

In the embodiment shown in Figures 19 to 22 the coupling is constructed differently from 130 1 593 089 that of Figure 13 The coupling member 93 is substantially identical to that shown in Figure 13 but it is connected by a shear pin 110 with a coupling member 126 differing from the coupling member 92 The coupling member 126 is fastened by means of a plurality of bolts 127 to a fastening portion 128 having a substantially circular circumference and serving to receive the fork parts 91 To the fastening part 128 is secured a carrier 129, the function of which is comparable with that of the carrier 99 and which is located between the fastening part 128 and the cutting ring 104 The carrier 129 has two cavities or recesses 131 disposed diametrically opposite each other about a centre line 130 These cavities 131 receive a plurality of shear pin holders Each cavity receives, for example, five cylindrical holders 132 each containing a shear pin 110 Each holder 132 comprises a sleeve of synthetic resin, for example, a plastic tube The holder covers the whole space between the fastening part 128 and the cutting ring 104 Near the cutting ring 104 the holder is provided on its inside with a tapering inner ring 133 constituting both a guide for the shear pin 110 and a stop for a widened part of a pressure pin 134 largely corresponding with the pressure pin 124 of Figure 18 The closure of the holder on the side of the end portion of the spring 123 is similar to that of Figure 18 The cap is fixed in place by means of a retaining pin The holders 132 are enclosed in the cavity 131 by means of an arcuate cover 136, which is concentric with the centre line 130 and the axial sides of which are bent over to form lugs 137 The lugs 137 co-operate with clamping springs 138, having a number of turns which surround the bolts 127 and press the cover 136 towards the centre line 130 In order to limit movement of the cover with respect to the spring 138 each lug 137 has ridges 139.

In this embodiment the pin 110 is in its connecting positions located in the opening 114 referred to in the preceding embodiment, this opening being bounded at one end, with respect to the direction of rotation B, by a cutting plate or disc 70 similar to the disc 64 of Figures 8 and 9 (see Figure 21) At the end of the opening 114 remote from the cutting plate 70 a filling plate 140 is connected with the coupling member 93 by nut and bolt connection The dimension 141 of Figure 21 is preferably 16 mms, and on this basis the filling plate 140 has the following dimensions 141 a and 141 b:

Shearpin diameter 141 a 141 b 7 mms 20 0 mms 28 0 mms 8 mms 18 5 mms 26 5 mms 10 mms 15 5 mms 23 5 mms The operation of the coupling shown in Figures 19 to 22 largely corresponds with that of the preceding embodiments The coupling can be readily filled with shear pin holders 132, which can be easily fixed in place by the cover 136 and the springs 138 With different pin diameters the fact T in the formula S = 'S A T 2 (the factor T being essentially determined by the pin diameter and the associated circumferential width 141 of the opening 114) can be 70 kept constant in this embodiment since the filling place 140 can be exchanged.

Figures 23 and 24 show an alternative embodiment of a breaking coupling, in which a shear pin 142 largely similar to the shear pin 75 of Figure 13 is provided with a groove 143 extending parallel to its longitudinal centre line throughout or substantially throughout the length This groove co-operates with a corresponding key 144 provided on the pin guide 80 means, for example, the sleeve 113, the centering plate 105 and the cutting ring 104 of Figure 13 The key 144 prevents the breaking pin from turning with respect to the rest of the coupling 85 The subject-matter of this application also forms part of the subject-matter of our copending patent application No 45291/77 (Serial No 1 593 088).

Claims (8)

WHAT WE CLAIM IS: 90

1 An overload coupling suitable for use in a rotary drive mechanism, the coupling comprising two members which are rotatable about a common axis, and at least one frangible element, which is disposed at least partly in a 95 holder connected for rotation with one of the member, the frangible element being capable of co-operating, in normal operation when in a connecting position, with the other member to interconnect the members for rotation together 100 in at least one direction, the members being relatively rotatable subsequent to fracture of the frangible element upon overload of the coupling, until the same or another frangible element takes up a connecting position in 105 which the interconnection of the members is re-established, at least part of the holder being releasably connected to the said one member by a quick-release connection.

2 An overload coupling as claimed in claim 110 1, in which the holder is provided with guide means for guiding the frangible element in its movement from one connecting position to another.

3 An overload coupling as claimed in 115 claim 1 or 2, in which the said one member is provided with locating means for locating the holder with respect to the said one member.

4 An overload coupling as claimed in any one of the preceding claims, in which the 120 frangible element is capable of re-establishing the interconnection of the members a plurality of times after successive overloads.

An overload coupling as claimed in any one of the preceding claims, in which the 125 holder is at least partly arcuate, the centre of the arc lying on the axis of rotation of the two members, and constitutes a housing for at least two frangible elements arranged side by side.

6 An overload coupling as claimed in any 130 one of the preceding claims, in which the holder is one of at least two identical holders which are connected to the said one member at locations which are diametrically opposite each other.

7 An overload coupling as claimed in any one of the preceding claims, in which the or each frangible element comprises a shear pin.

8 A shaft having at least one universal joint and at least one overload coupling as claimed in any one of the preceding claims.

1 593 089 HASELTINE LAKE & CO.

Chartered Patent Agents, 28 Southampton Buildings, Chancery Lane, London WC 2 A 1 AT.

and Temple Gate House, Temple Gate Bristol BSI 6 PT.

and 9 Park Square Leeds L 51 2 LH Printed for Her Majesty's Stationery Office by MULTIPLEX techniques ltd, St Mary Cray, Kent 1981 Published at the Patent Office, 25 Southampton Buildings, London WC 2 l AY, from which copies may be obtained.