AU694806B2

AU694806B2 - Overload protection mechanism

Info

Publication number: AU694806B2
Application number: AU37806/95A
Authority: AU
Inventors: Stan Westcott
Original assignee: AUSTRALIAN SOIL CARE SYSTEMS P
Current assignee: AUSTRALIAN SOIL CARE SYSTEMS PTY Ltd
Priority date: 1993-12-23
Filing date: 1995-11-10
Publication date: 1998-07-30
Anticipated expiration: 2015-11-10
Also published as: AU3780695A

Description

4.

AUSTRALIA

Patents Act 1990 AUSTRALIAN SOIL CARE SYSTEMS PTY LTD

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title.- Over-load piotection mechanism The following statement is a full description of this invention including the best mnethod of performing it lImown to us:i ~arrPazeu OVERLOAD PROTECTION MECHANISM Technical Field The present invention relates to an overload protection mechanism in which a shear pin is utilised to extend through aligned apertures in two juxtaposed or closely spaced members. The shear pin prevents relative movement between the members until an overload force is applied to one of them which caused shearing of the shear pin and relative movement between the members.

Technological Background Shear pins are one of the cheapest and simplest means for the protection of parts of all sorts of machinery or apparatus from damage or destruction due to the application of overload forces ie, forces greater than those which the machinery or apparatus is designed to withstand. Such shear pins may be held in position in a number of different ways and the most suitable way will vary from application to application. Many of the known location and retention mechanisms for shear pins are unnecessarily i complex or involve a degree of precision in the parts that is, in practice, difficult to achieve, The positioning of the shear pin relative to the parts adapted to move 0 relative to one another in an overload situation is particularly important where the shear pin is provided with a peripheral groove or grooves to define to# one or more planes of preferred shearing each having a predetermined shear strength capable of withstanding up to the predetermined overload force, In this case, if the tolerances are not close, it is possible for the shear pin to 25 move relative to the members along its own longitudinal axis. This would r cause the preferred plane of the shear pin to be displaced from, and the full cross-sectional area of the pin to be aligned with, the parting faces of the .members such that the shear pin will then not shear under a designated overload force and damage to the machinery or apparatus may result.

4 30 Disclosure of the Invention The present invention consists in an overload protection mechanism comprising a shear pin extending through aligned apertures in two juxtaposed or closely spaced members which are adapted to move relative to one another along a parting plane upon the application of an overload force to one of them, the shear pin having a groove extending around at least a part of its periphery transversely of its longitudinal axis and defining a 016 3 preferred shear plane having a predetermined shear strength, a resilient substantially annular element disposed in the groove of the shear pin and projecting from the groove around at least a part of the periphery of the shear pin, the shear pin being so located in the apertures that the groove and the resilient element lie in the parting plane between the two members and the engagement of the resilient element with the members on either side of the parting plane substantially prevents movement of the shear pin relative thereto, The overload protection mechanism according to the present invention may be used in a wide variety of applications. It is, however, of particular applicability in the construction of ground engaging implements such as ploughs and rippers where the component members are formed by casting or otherwise involve parts made to relatively low tolerances. Shear pins for use in the present invention will normally be of circular crosssection although they could be of any suitable cross-sectional shape eg, square or hexagonal. The groove or grooves will normally extend around the full circumference of a circular cross-section shear pin, however, in the case of pinls of other cross-sectional shapes it or they may not be continuous. The groove or grooves will also normally lie in a plane or planes normal to the longitudinal axis of the shear pin however this is not essential. What is required is that, in use, the groove(s) will be located in the parting plane(s) between the two or more members.

~The groove or grooves may be V-shaped in longitudinal section of the pin, or could be in the form of a semi-circle or have a rounded bottom. The 25 groove should be deep enough so that the resilient element will be firmly S: engaged in the groove while protruding beyond the outside surface of the shear pin about at least a part of the perimeter of the shear pin. In the case that the shear pin is circular in cross-section, the resilient element will preferably project around the full circumference of the shear pin. The 4 30 degree to which the resilient element protrudes beyond the outside surface 30 ft,, of the pin will depend upon the amount of clearance there is between the S" pin and the apertures. The resilient element is designed to project beyond 4 fftthe outside surface of the shear pin a distance which is sufficient for it to be engaged between the members on either side of the parting plane and to be held in place by that engagement. The retention of the element in place serves to hold the groove(s) of the shear pin in alignment with the parting i CCL i4 plane(s) between the members. The resilience of the element dampens vibrations and limits them from being transmitted to the shear pin. Any tendency for the pin to migrate along the apertures is thereby minimised or stopped. The groove or grooves are thus always retained in the correct position and the possibility for the full cross-section of the shear pin to be positioned across the parting plane rather than the reduced diameter at the groove is eliminated or at least greatly reduced.

i The resilient element preferably has a complete annular form and i may be an O-ring formed of rubber or a suitable elastomeric synthetic plastics material. It could however comprise a suitable open spring, a spiral wound metal spring, or a string or tape of a suitable resilient material wound around the groove until it is of an appropriate thickness. For example, the resilient element may be an open spring in the form of C-clip or the like of metal, rubber, plastic or other suitable resilient material, and which has sufficient rigidity to retain itself within the groove. It will also be appreciated that it is not necessary for the radially projecting part or parts of Sthe resilient element to be continuous around the pin, and instead may be in i the form of at least one radially projecting part. Preferably there are a 2 i plurality of radially projecting parts positioned at spaced locations around i 20 the groove, and more preferably there is one or more projections which is/are substantially continuous around the groove.

The arrangement according to this invention has the substantial advantage that the shear pin need not project beyond the outside faces of the members and the amount of material in the shear pin is thus reduced to a minimum. A further advantage in that the pin is easy to place and remove, It is only necessary to align the apertures in the members and push the shear pin into place, A third advantage is that O-rings and other suitable resilient annular elements are cheaper than almost any other conceivable retaining element for the shear pin.

The overload protection mechanism according to this invention can be used in place of conventional shear pins in almost any situation in which a shear pin extends through aligned apertures in two members separated by a parting plane. It is, however, desirable to round, chamfer or otherwise cut the edges of the apertures to avoid sharp edges which may cut into the resilient annular element.

I Brief Description of the Drawings I-Iereinafter given by way of example only is a preferred embodiment of the present invention described with reference to the accompanying drawings wherein: Figure 1 shows, in a partly cut away form, a perspective view of an overload protection mechanism according to the present invention; and Figure 2 shows a detailed sectional view along line A-A of Fig. 1.

Best Mode of Carrying out the Invention A moveable ripper blade 10 (only the upper part of which is shown) is disposed between a pair of frame members 11 (only parts of which are shown). A parting plane 12 exists between each of the juxtaposed faces of the blade 10 and the frame members 11. In the event that an overload force is applied to the ripper blade 10 it will be moved relative to the frame members 11 along the parting planes 12. The blade 10 and the frame members 11 each have an aperture 13. In the normal operating situation the apertures 13 are aligned.

Ani elongate shear pin 14 extends through the apertures 13 to retain the blade 10 in its normal working relationship to the frame members 11.

The pin 14 is cylindrical with two spaced apart V-section grooves extending around its circumference in parallel planes normal to the longitudinal axis of the pin 14, The grooves 15 define preferred shear planes having a predetermined shear strength which will be overcome when a predetermined overload force is exerted between the upper blade 10 and the frame members 11. The grooves 15 are spaced apart by a distance equal to the distance between the parting planes 12, An 0-ring 16 is disposed in each of the grooves 15 so as to be retained thereby, and are of such an outside diameter that they protrude out of their respective grooves 15 beyond the outside surface of the pin 14 a distance which is sufficient for it to be received in the space 17 of the parting plane 12 and engaged between the blade 10 and the frame 11, In use the shear pin 14 is positioned in the aperture 13 so that the 0rings 16 are disposed, and cooperate with, in the parting planes 12 to retain the pin 14 in that position. This ensures that the grooves 15 are always correctly aligned with the parting planes 12.

L 6 More particularly, the parting plane 12 between the members 10, 11 will be in the form of a narrow space 17 and the radially projecting portion 16a of the O-ring 16 locates itself in this space 17. In order to prevent the O-ring 16 from being damaged by the outside edges 13a of the apertures 13 which are adjacent the parting plane 12, it is desirable for these edges 13a to be rounded, chamfered or other wise cut to remove any sharp edges. This further defines the space 17 within which the 0-ring 16 nestles for securely locating the shear pin 14 relative to the blade 10 and frame members 11.

It will be appreciated that the blade 10 and the frame members 11 are initially caused to be arranged with the apertures 13 in a linear array. In this way the shear pin 14 can be pushed into place in the apertures 13 until the O-rings 16 nest into the spaces 17 of the partilg planes 12 and engage with the blade 10 and the frame member 11 on each side of the respective parting plane 12.

When the shear pin 14 is being pushed into the apertures 13, the 0rings 16 will be compressed while they are within the apertures 13, and will be allowed to at least partly expand into the space 17 when they are aligned with the respective parting planes 12, If an overload situation occurs the shear pin 14 will shear in the preferred shear planes defined by the two grooves 15, and the blade 10 will pivot on a pivot pin (not shown) clear of the obstruction causing the overload force, The broken parts of the shear pin 14 may then be readily removed and, after realignment of the apertures 13 in the blade 10 and the frame members 11, a new shear pin 14 is positioned in o the apertures 13.

It will be appreciated by persons skilled in the art that numerous Svariations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

a oa 4 1 1

Claims

1. An overload protection mechanism comprising: a shear pin extending through aligned apertures in two juxtaposed or closely spaced members which are adapted to move relative to one another along a parting plane upon the application of an overload force to one of them; the shear pin having a groove extending around at least a part of its periphery transversely of its longitudinal axis and defining a preferred shear plane having a predetermined shear strength; and a resilient substantially annular element disposed in the groove of the o shear pin and projecting from the groove around at least a part of the c.'o periphery of the shear pin; 0 te wherein the shear pin is so located in the apertures that the groove and °o0the resilient element lie in the parting plane between the two members and 15 the engagement of the resilient element with the members on either side of the parting plane substantially prevents movement of the shear pin relative thereto.

2. The mechanism of claim 1 wherein the groove extends around the full circumference of the shear pin to define an annular recess. 20 3. The mechanism of claim 2 wherein the shear pin is generally cylindrical. o« 4. The mechanism of claim 2 wherein the groove lies in a plane generally normal to the longitudinal axis of the shear pin. The mechanism of claim 2 wherein the groove has a V-shape, a semi- circular shape or a rounded bottom in longitudinal section of the shear pin.

6. The mechanism of claim 2 wherein the resilient element has a complete annular form.

7. The mechanism of claim 6 wherein the element is an O-ring formed of rubber or a suitable elastomeric synthetic plastics material,

8. The mechanism of claim 1 wherein the resilient element is an open spring element in the form of a C-clip or the like of metal, rubber, plastic or other suitable resilient material,

9. The mechanism of claim 6 wherein the resilient element is a spiral wound spring element, i K; 8 The mechanism of claim 6 wherein the resilient element is formed by a string or tape of suitable resilient material wou' i around the groove until it has an appropriate thickness.

11. The mechanism of claim 1 wherein the shear pin has a length approximately equal the combined length of the apertures in the members.

12. The mechanism of claim 1 wherein edges of the apertures in the members adjacent the parting plane are chamfered, rounded or otherwise cut to define an annular space lying in the parting plane within which the reilient element nestles.

13. An overload protection mechanism comprising: a shear pin extending through aligned apertures in three juxtaposed or closely spaced members, comprising a middle member disposed between two ,oo, outer members, the middle member being adapted to move relative to the Sa outer members along parting planes upon the application of an overload force o" h idl m 15 to the middle member; "the shear pin having a first groove extending around at least a part of its periphery transversely of its longitudinal axis and defining a first preferred shear plane having a predetermined shear strength, and having a .second groove spaced from the first groove and defining a second preferred 20 shear plane having a predetermined shear strength; and two resilient substantially annular elements disposed one in each groove of the shear pin and projecting from the groove around at least a part of the periphery of the shear pin; acte,. wherein the shear pin is so located in the apertures that one groove and the resilient element disposed therein lie in the parting plane between the middle member and one of the outer members, and the other groove and the resilient element disposed therein lie in the parting plane between the middle member and the other outer member, and wherein the engagement of each of the resilient elements with the members on either side of the parting planes substantially prevents movement of the shear pin relative thereto,

14. The mechanism of claim 13 wherein the grooves extend around the full circumference of the shear pin to define an annular recess. The mechanism of claim 14 wherein the shear pin is generally cylindrical.

16. The mechanism of claim 14 wherein each groove lies in a plane generally normal to the longitudinal axis of the shear pin, ik, VY I~,

17. The mechanism of claim 14 wherein each groove has a V-shape, a semi-circular shape or a rounded bottoirn in longitudinal section of the shear pin.

18. The inechanism of claim 14 wherein the resilient elements have a complete annular form.

19. The mechanism of claim 18 wherein the elements are 0-rings formed of rubber or a suitable elastomeric synthetic plastics material. The mechanism of claim 13 wherein the resilient elements are an open spring element in the form of a C-clip or the like of metal, rubber, plastic or other suitable resilient material.

21. The mechanism of claim 18 wherein the resilient element is a spiral wound spring element.

22. An overload protection member as claimed in any one of claims 13 to 21 with reference to and as shown in Figures 1 and 2 of the drawings. 00 0 00 0 0000 0 0 0 0 0000 o 00 00 Q 0 0 00 0 000 00 00 00 0 0 0 00 00 0 0 00 0 0 0 09 00 0 DATED this tenth day of June 1998 AUSTRALIAN SOIL CARE SYSTEMS PTY LTD Patent Attorneys for the Applicant: 00.000.B. RICE CO. #.Go 4 ABSTRACT An overload protection mechanism which includes a shear pin (14) extending though aligned apertures (13) of two or more juxtaposed or closely spaced members (10,11) which move relative to one another along a parting plane (12) upon application of an overload force to one of them. The shear pin (14) has a groove (15) extending around its periphery and transversely of its longitudinal axis so as to define a preferred shear plane having a predetermined shear strength. The groove (15) has an O-ring (16) disposed therein which projects a predetermined distance beyond the outside surface of the shear pin (14) which is sufficien't for it to engage with the members (10,11) on each side of the parting plane The projecting part (16a) of the O-ring 16 nestles in the space (17) of the parting plane (12) between the two members (10,11) so as to locate, and substantially prevent movement of, the shear pin (14) relative to the members (10,11). In this way, the preferred shear plane of the pin (14) is kept in alignment witlh i iarting plane (12) of the members (10,11). 0 |4