GB2177479A

GB2177479A - Lock and release device for couplings

Info

Publication number: GB2177479A
Application number: GB08613780A
Authority: GB
Inventors: Charles Henry Hatton
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1985-06-27
Filing date: 1986-06-06
Publication date: 1987-01-21
Also published as: GB8516295D0; GB8613780D0

Abstract

A lock and release device 10 for use in an assembly 24 of components 26, 28, 30 coupled together by screwthreads has two members in the form of discs 12. Each disc 12 has a plurality of helical cam surfaces 16 which are complementary to and cooperate with the corresponding surfaces 16 on the other disc 16. The helix angle of the surfaces 16 is greater than the helix angle of the threads of the assembly 24. Relative rotation of the discs 12, for example caused by frictional engagement with the ends of the shafts 26, 28 of the assembly 24 as torque is applied to tighten or loosen the assembly 24, causes the device 10 to increase or decrease in thickness thereby to lock or release the assembly 24. <IMAGE>

Description

SPECIFICATION Lock and release device for use in an assembly of components The invention relates to a lock and release device for use in an assembly of components coupled together by screw threads particularly, though not exclusively, for screw-threaded couplings used for transmitting torque.

There are many applications in which screwthreaded couplings are used to transmit torque.

One typical application is the shafts used with bore hole pumps. Such shafts can be several hundred metres in length and are made up from shorter sections coupled together by screw-threaded couplings. In service, the torque transmitted by the shaft is in a sense which tends to tighten the couplings even more.

Consequently, if it is required to de-couple the shaft sections it is usually necessary to apply a torque greater than that applied to the couplings during assembly of the shaft. In some circumstances, particularly when larger pumps are involved, it may be difficult to unscrew the couplings using the equipment normally available on a site thereby either creating an expensive delay in the operation whilst special equipment is obtained or creating an increased capital expenditure to provide special equipment which may be used only infrequently.

Similar problems can arise in other applications involving screw-threaded components which transmit torque.

In other forms of screw-threaded components, it is also desirable that they can be uncoupled with relative ease.

It is an object of the invention to provide a lock and release device for an assembly for components coupled together by screw threads whereby the torque required to de-couple the assembly is no greater than the torque applied during assembly.

According to the invention, a lock and release device for use in an assembly of components coupled together by screw threads, which device comprises two members, at least one member comprising a disc having on one side a plurality of helical cam surfaces the helix angle of which is greater than the helix angle of the threads of the assembly and the other member having complementary helical cam surfaces which cooperate with the cam surfaces on said one member, relative rotation of the members with the respective cam surfaces engaged with one another varying the thickness of the device whereby torque applied in a sense to tighten or to loosen the components of the assembly respectively increases or decreases the thickness of the device.

Preferably, the members are identical to one another. Alternatively, said other member comprises a component of the assembly.

Preferably, the or each disc has on the other side thereof friction means for engaging a surface of one component of the assembly.

Preferably, the or each disc is annular.

Preferably, each cam surface of each member is separated from adjacent cam surfaces by radiallyextending grooves.

Preferably, engaged pairs of the cam surfaces are separated from adjacent pairs by resilient material which is preferably bonded to the members.

The invention includes an assembly of components coupled together by screw threads which assembly incorporating a lock and release device as hereinbefore defined.

A lock and release device for and an assembly of components coupled together by screw threads and incorporating the device will now be described to illustrate the invention by way of example only with reference to the accompanying drawings, in which: Figures 1 to 4 are respectively an elevation; a view on arrow A in Figure 1; a view on arrow B in Figure 1; and a perspective view of a member of the device; Figure 5 is an elevation of two members of the type shown in Figures 1 to 4 assembled together as the device; and Figure 6 is a longitudinal section of the assembly incorporating the device shown in Figure 5.

The lock and release device 10 (Figures 5 and 6) has two identical members in the form of annular discs 12 (see particularly Figures 1 to 4).

Each disc 12 has been machined on one side to provide a knurled surface 14 for frictionally engaging a respective opposed surface of components of the assembly 24. The opposite side of the disc 12 is provided with helical cam surfaces 16 disposed in a circular arrangement concentrically with the centre 18 of the disc. The helix angle of the surfaces 16 is greater than the helix angle of the threads of the assembly 24. For ease of machining the surfaces 16, each cam surface 16 is separated from adjacent surfaces 16 by radially-extending grooves 20.

As can be seen from Figures 5 and 6, when two discs 12 are assembled together to form the device 10, engaged pairs of the cam surfaces 16 are separated from adjacent pairs by resilient material 22, typically silicon rubber, injected therebetween.

Conveniently, the resilient material is keyed into the grooves 20 and bonds the two discs 12 together.

The assembly 24 (Figure 6) is in the form of a coupling having two shafts 26, 28 each terminating in a screw-threaded end and an internally screwthreaded sleeve 30 for receiving the ends of the shafts 26, 28.

The assembly 24 is assembled by screwing the sleeve 30 onto one of the shafts say 26, so that approximately half the threaded portion of the sleeve remains free to receive the end of the other shaft 28. The device 10 is then located inside the sleeve on the end surface 32 of the shaft 26.

The shaft 26 is then screwed into the sleeve 30 so that the end surface 34 thereof engages the device 10.

Torque is applied to the shafts 26, 28 to tighten the assembly 24. The applied torque causes the knurled surfaces 14 of the discs 12 to frictionally engage and bite into the end surfaces 32, 34 of the shafts 26, 28, respectively. The frictional engagement of those surfaces cause the discs 12 to rotate relatively to one another such that the engaged pairs of cam surfaces 16 rides up one another to increase the thickness of the device 10 which places the assembly 24 in tension and enables it to transmit torque. Thus, the shafts 26, 28 and the sleeve 30 of the assembly 24 are locked together in torque trasmitting relationship by the device 10.

The change in the angular relationship between the discs 12 is relatively small and no attempt has been made to show such change in Figure 6.

If it is required to dismantle the assembly 24, torque is applied to the shafts 26, 28 in an opposite sense to the tightening torque which causes the engaged pairs of cam surfaces 16 to ride down one another to decrease the thickness of the device 10 thereby relieving tension in the coupling 24. As the helix angle of the cam surfaces 16 is greater than the helix angle of the threads of the assembly 24, the tension in the assembly 24 is suddenly released at a torque lower than the torque applied during assembly of the assembly 24. Tests have shown that the torque required to release the tension in the assembly 24 can be as low as 25% of the torque required to tighten the assembly 24.

The ratio of coupling torque to releasing torque can be controlled by adjusting the helix angle of the cam surfaces 16.

It will be appreciated that, owing to the engaged pairs of cam surfaces 16 forming a partial key-type engagement between the shafts 26, 28, the tension in the assembly 24 for a given applied torque is lower than the tension in the coupling 24 when the device 10 is omitted. That fact enables the assembly 24 either to transit higher torques or to be made of smaller components for a given torque rating.

The surface area of the cam surfaces 16 is selected to be sufficient to withstand the crushing stress imposed by the applied torque.

The surface 14 of each disc 12 has to be harder than the opposed, abutting surfaces in the components of the assembly in order that a sufficient frictional engagement can occur between those surfaces. The surface 14 can have for example teeth or other formations for ensuring adequate frictional engagement between those surfaces.

In a modification, frictional engagement between those surfaces may be dispensed with. In that instance, relative rotation between the discs 12 can be achieved from externally of the assembly 23, e.g. by means of lever bars engageable with radial holes in the discs 12 or any other suitable means.

The provision of the resilient material 22 to maintain adjacent pairs of engaged cam surfaces 16 separate from one another, ensures that the pairs of cam surfaces 16 can always ride down one another sufficiently to release the tension in the assembly 24, the material 22 being compressed.

The device can be used in many applications, including applications in which no torque is to be transmitted by the assembly, and the components of the assembly can take many forms, e.g. a fan or pump impeller screwed onto a drive shaft, a drill chuck, a milling arbor, a vice.

In a modification, one member of the device 10 can be one of the components of the assembly, the cam surfaces 16 being machined on the relevant component, e.g. one the end of one shaft 26, 28 in the assembly 24.

Claims

1. A lock and release device for use in an assembly of components coupled together by screw threads, which device comprising two members, at least one member comprising a disc having on one side a plurality of helical cam surfaces the helix angle of which is greater than the helix angle of the threads of the assembly and the other member having complementary helical cam surfaces which cooperate with the cam surfaces on said one member, relative rotation of the members with the respective cam surfaces engaged with one another varying the thickness of the device whereby torque applied in a sense to tighten or to loosen the components of the assembly respectively increases or decreases the thickness of the device.

2. A device according to claim 1, in which the members are identical to one another.

3. A device according to claim 1, in which said other member comprises a component of the assembly.

4. A device according to any one of the preceding claims, in which the or each disc has on the other side thereof friction means for engaging a surface on one component of the assembly.

5. A device according to any one of the preceding claims, in which the or each disc is annular.

6. A device according to any one of the preceding claims, in which each cam surface is separated from adjacent cam surfaces by radially-extending grooves.

7. A device according to any one of the preceding claims, in which engaged pairs of the cam surfaces are separated from adjacent pairs by resilient material.

8. A device according to claim 7, in which the resilient material is bonded to the members.

9. A device according to claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

10. An assembly of components coupled together by screw threads comprising at least two components coupled together by cooperating screw threads, the assembly incorporating a lock and release device as claimed in any one of the preceding claims.