COIL SPRING

Abstract: A coil spring has bridging portions (B) distributed substantially uniformly about the annular clearance between alternating major diameter coils (C1) and minor diameter coils (C2) along its length.

Description: COIL SPRING The invention relates to a coil spring. It is one object of this invention to provide a coil spring which is particularly versatile in use. According to the invention in one aspect there is provided a coil spring comprising a length of wire or the like, having the shape of a point travelling along a continuous generally helical path to define major diameter coil portions and minor diameter coil portions, the portions alternating along the length, the length of wire bridging one major diameter coil and the next minor diameter coil extending across the annular clearance in between the coils and arranged to accept radial forces. Preferably the major diameter coils and the minor diameter coils are substantially concentric. Preferably the portions alternate diametrically along the length. Most preferably the bridging lengths are substantially uniformly distributed about the annual clearance along the length of the spring. In one embodiment the bridging length between successive major diameter coil portions and minor diameter coil portions is rotated by about one-third of a turn whereby three equally spaced bridging lengths are formed along the length of the spring. In another variation there are five bridging lengths. The number of bridging lengths is not critical to the invention. In another aspect the invention provides a method of making a spring from a length of wire or the like, the method comprising forming at least one coil of a first diameter, turning the length trailing the first coil a short distance and then forming at least one coil of a second diameter, turning the length training the second coil a short distance and then forming at least one coil of the first diameter; whereby to form a spnng having the shape of a point travelling along a continuous generally helical path to form major diameter coil portions and minor diameter coil portions, the portions alternating along the length, the length of wire bridging one major diameter coil and the next minor diameter coil extending across the annular clearance between the coils and arranged to accept radial forces. Preferably the method is applied to a continuous length of wire using a computensed numeπcally controlled (CNC) spnng making machine to produce successive spπngs which are cut off when formed The spnngs can of course be produced by other suitable methods. The spnng element may be made of music wire, or wire which is square or rectangular or of any other appropriate material and shape The ends of the element may be provided with connectors, e.g. hooks, loops, eyes, flats, pigtails, bolts, or the like Length portions may include flats for keying, etc , a coating, e.g of an elastomenc material may be present on one or more coil portions. A spπng element of the invention compπses in effect two spπngs, one within the other and which are joined together by the bπdging portions. Depending on the circumstances of use each bridging length can act as a compression, torsion, shear, or tensile member. In another aspect the invention provides an assembly of two members, incorporating a spring as defined, wherein either the major diameter coil portions or the minor diameter coil portions are held and the other is free to move, the bridging lengths acting as spπng members. In one use a spring of the invention may be received, e.g. trapped in a socket corresponding to the outside diameter of the spring, and a shaft is inserted through the passageway defined by the minor diameter portions of the coil. The spring can then act as an alignment aid for interchangeable tooling, allowing for say 1-2 mm lateral adjustment on a 6 mm diameter shaft. The spring will naturally return the shaft to the centre of the socket because of the resilient mounting of the bridging portions and unlike a rubber member it may not take a permanent set. It is especially useful in robotics where the gripper on the robot arm is mounted via these springs, and has to pick up parts from mould tools and place them onto secondary equipment. In such a case pilot pins on the gripper locate into bushes on both the mould tool and secondary machine, with the springs allowing for a degree of misalignment without transmitting shocks onto the robot arm. A spπng of the invention is also useful for anti-vibration damping of equipment, with the advantage of being adaptable to suit the application. It may also be used to self centre in other cases such as a control or like device in a socket, e.g. as in a joystick for computer equipment. Springs of the invention can also be used as fixing and fastening inserts for example between components to be joined in face-to-face relation. If springs elements of similar diameters are received in plain holes in the facing components a pin of slightly larger diameter than the diameter of the coil internal diameter can be pushed in, and in doing so will expand the end of the coils and lock in position (The pin could be removed by rotating and pulling at the same time) Another use is to retain screws into plasterboard or like mateπal. If a spring of the invention inserted into a plain drilled hole in plasterboard then an appropriately sized tight fitting screw could be inserted into it, urging the outside diameter radically outward, allowing it to compress the plaster without cutting a thread directly into it It would act like a wall plug but the radial grooves should give it an improved retention. A spπng of the invention may also be used in other applications For example as a shaft coupler to take out mis-alignments from rotating equipment where the internal bore and the external diameters would require a keying factor such as one or two flats to prevent rotation or as a trolley wheel, e.g. for a pallet truck, suspension member, that would use the basic spring to reduce vibration when used on rough surfaces This may also need a key feature on the internal bore, or as a "damping" device for traffic bollards, where they will deflect without inflicting too much damage, and for waterway applications (locks etc.) relieve the forces on ropes. The spring may also be used in an article of furniture. In another aspect the invention provides an assembly between the two members (such as an exhaust pipe and the mounting therefor) to allow for relative movement between the members because of relative thermal expansion. In yet another aspect the invention provides a vehicle suspension system incorporating a spπng according to the invention In order that the invention may be well understood it will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which- Figure 1 is a side elevation of one spring of the invention; Figure 2 is a partial view taken on arrow A on Figure 1 ; Figure 3 is a sectional view taken on lines Ill-Ill on Figure 1 showing the spring received in a socket and containing a rod; and Figure 4A is an end elevation and Figure 4B is a longitudinal section of the spring element in use as a shaft coupler. The spring element of Figures 1 to 3 comprises a continuous or single length of 0.8 mm diameter music wire bent into shape using computerised numerically controlled machinery. The length comprises alternating major diameter coils C1 and minor diameter coils C2. The coils are concentric. In one example the major (outer) diameter is 11.60 mm and the inner diameter 6.00 mm, leaving a notional annulus in between. As shown in Figure 1, at the left hand end there is a complete major diameter coil C1 which extends into a bridging or transition portion B which then merges into a minor diameter coil C2. This leads to another bridging portion B which in turn leads to the next major diameter coil C1. Further bends are formed in the wire to form diametrically alternating major and minor coils. It will be observed that there is a radial distance between the outer margin of a minor coil C2 and the inner margin of major diameter coil C1. This forms a discontinuous or interrupted annular clearance along the length of the spring with a continuous transition between the major diameter coil portions and the minor diameter portions. The bridging portions B extend like radial spokes across the annular gap, along the length of the spring. To ensure that the bridging portions are evenly distributed about the annulus there is a transition every 1 3 tum (but of course this value is not essential to the invention). In this way two coaxial spring lengths are formed but joined together by radially spaced apart bridging portions B. The spring of Figures 1 and 2 is made using a CNC multislide spring winding machine. The length of wire, e.g. music wire, is coiled except that after the last tum to form one or more coils of a predetermined diameter a short length (herein called the transition) is left before the wire is coiled at the second diameter. These continuous transition lengths form the bridging portions or radial spokes of the spring. The length of the transition may be varied, e.g. to be 1/3 or 1/5 of a tum dependant on the number of radial spokes or bridging portions are appropriate to the intended end use of the spring. One particularly useful advantage of a spring of the invention is that depending on the design it may be telescoped to approximately half its lengths. The spring of Figures 1 and 2 can be used as an alignment aid, as shown in Figure 3. A plain hole socket is formed in a support S and the spring is received therein. The major diameter coils C1 contact the inner wall of the socket. A shaft or like rod R is inserted in the aligned minor diameter coils C2 and will be tightly grasped thereby, then tension being taken up by tensional movement of the bridging portions B. The element can be used for the other purposes. It is of particular advantage to use the element to receive a screw in a plasterboard or the like because the major diameter coils C1 can engage the wall of the socket without forming a thread. In the embodiment of Figures 4a and 4b both sets of coils include flat retention portions 20 to as a key to prevent rotation within a cylindrical passageway. The invention is not limited to the embodiments shown. The number of coil portions may vary as may transition lengths. The number of flats may be varied. Blocks or pads or coatings of elastomeric material may be present on one or more coil portions.

Claims: CLAIMS 1. A coil spring comprising a length of wire or the like, having the shape of a point travelling along a continuous generally helical path to define major diameter coil portions and minor diameter coil portions, the portions alternating along the length, the length of wire bridging one major diameter coil and the next minor diameter coil extending across the annular clearance in between the coils and arranged to accept radial forces. 2. A spring according to Claim 1 , formed of a single length of wire. 3. A spring according to Claim 1 or 2, wherein the bridging lengths are substantially uniformly distributed about the annual clearance. 4. A spring according to any preceding Claim, wherein the bridging length between successive major diameter coil portions and minor diameter coil portions is rotated by about one-third of a turn whereby three equally spaced bridging lengths are formed along the length of the spring. 5. A spring according to Claim 1 to 3, wherein the bridging length between successive major diameter coil portions and minor diameter coil portions is rotated by about one-fifth of a turn whereby five equally spaced bridging lengths are formed along the length of the spring. 6. A spring according to any preceding Claim, wherein the major diameter coils and the minor diameter coils are substantially concentric. 7. A spring according to any preceding Claim, wherein the wire is music wire or the like. 8. A spring according to any preceding Claim, having a coating on one or more coil portions. 9. A spring according to any preceding Claim, adapted to compress longitudinally to about half its uncompressed length. 10. A method of making a spring from a length of wire or the like, the method comprising forming at least one coil of a first diameter, turning the length trailing the first coil a short distance and then forming at least one coil of a second diameter; turning the length trailing the second coil a short distance and then forming at least one coil of the first diameter; whereby to form a spring having the shape of a point travelling along a continuous generally helical path to form major diameter coil portions and minor diameter coil portions, the portions alternating along the length, the length of wire bridging one major diameter coil and the next minor diameter coil extending across the annular clearance between the coils and arranged to accept radial forces. 11. A method according to Claim 10, wherein the method is applied to a continuous length of wire to form successive springs. 12. A method according to Claim 10 or 11, wherein the method is applied to wire using a computerised numerically controlled (CNC) spring making machine. 13. A method according to Claim 10, 11 or 12, wherein the bridging length between successive major diameter coil portions and minor diameter coil portions is rotated by about one-third of a turn whereby three equally spaced bridging lengths are formed along the length of the spring. 14. A method according to Claim 10, 11 or 12, wherein the bridging length between successive major diameter coil portions and minor diameter coil portions is rotated by about one-fifth of a tum whereby five equally spaced bridging lengths are formed along the length of the spring. 15. An assembly of two members, incorporating a spring according to any of Claims 1 to 9, wherein either the major diameter coil portions or the minor diameter coil portions are held and the other is free to move, the bridging lengths acting as spring members. 16. An assembly according to Claim 15, comprising a first member having a socket, the spring being received in the socket with the major diameter coil portions in engagement with the wall of the socket, and a second member received in the minor diameter coil portions of the spring, the bridging lengths of the spring acting to locate the second member in a predetermined position. 17. An assembly according to Claim 15, comprising two members each having a plain wall bore and arranged in face-to-face relation, a coil spring received in each bore, a pin having a diameter slightly larger than that of the minor diameter coil spring portion of the coil springs extending into the minor diameter coil spring portions of both coil springs whereby to fix the two members in the face-to-face relation. 18. An assembly according to Claim 15, wherein the coil spring is present between the two members (such as an exhaust pipe and the mounting therefor) to allow for relative movement between the members because of relative thermal expansion. 19. A vehicle suspension system incorporating a spring according to any of Claims 1 to 9. 20. An article of furniture including a spring according to any of Claims 1 to 9. 21. Apparatus including a control or like device, mounted in a socket, including a spring according to any of Claims 1 to 9 therein to self centre the device within the socket.

Inventors: DRISCOLL DAVID, DRISCOLL, DAVID
Applicants: DRISCOLL DAVID, DRISCOLL, DAVID
Application year: 1997
Main classification: F16F1
IPC codes: F16F1