GB2120788A - Shape memory member - Google Patents

Abstract

A member in the form of a plate (1) or the like has at least one slot (3) defining a movable portion (4) which moves in accordance with temperature by means of a shape memory effect. The member can be used as flow control means; a fastening device; or an actuator. The member may be actuated by passing an electric current through an electrically conducting flexible layer attached to the member and insulated therefrom by a further layer of material. <IMAGE>

Description

SPECIFICATION Shape memory members This invention relates to shape memory members. Such members can be used for example as thermal actuators, clamping rings, and in many other fields.

The shape memory effect is exhibited by various materials and consists essentially in that an element of such a material when formed to an initial shape and subsequently plastically deformed to another shape at an appropriate temperature, will automatically revert at least to a substantial extent to its initial shape at a different temperature or tend to do so depending on the degree of outside restraint to which the element is subjected.

Thus, such elements, in their deformed shape, can be subjected to heating and cooling through a transformation temperature range characteristic of the material, so as to cause a displacement towards their initial shape or tend to cause such a displacement and thus effect merely the exertion of a force on another member. The change can be made automatically reversible in relation to temperature changes.

The shape memory effect is particularly exhibited by certain alloys with a predominantly ss phase composition which experience a transformation from austenite at a relatively high temperature to martensite at a relatively low temperature, and the reverse transformation at a higher temperature. Such alloys include alloys of Ni-Ti, In-TI, Au-Cd, Ag-Zn, and (Ni1 XCux)-Ti. Particularly preferable alloys are of Cu with one or more of e.g. Zn, Al, Ni, Mn, Sn or Co.

In general, the use of the shape memory effect in the field of flow control has been in actuators for operating valve elements or the like. Whilst such arrangements have many advantages such as good sensitivity and rapid response, there remains the fact that the shape memory actuator is replacing a known actuator in a device which is otherwise relatively conventional. There has been proposed a carburettor jet of shape memory alloy, which varies in cross section with temperature. The changes involved would not however be of a great magnitude and in one proposal the contraction of the jet orifice over a temperature range of about 50"C is about 0.0003 inches (0.0008 cm]. One object of this invention is therefore to provide an improved means for flow control, utilising the shape memory effect.

The shape memory effect has also been proposed for use in the field of retainers, or fasteners. Thus clamping rings of shape memory alloy have been proposed, as have "C"shaped clamps. A further object of this invention is therefore to provide means which permits more versatile retaining or fastening arrangements.

A still further object of the present invention is to provide means which permits improved types of actuators to be constructed, for use in many different fields.

Thus, viewed from one aspect the invention provides a member of a-shape memory material having therein at least one slot defining, at least in part, a portion of the member adapted to move or tend to move in response to a change in temperature by means of a shape memory effect.

In the context of flow the arrangement will generally be such that the member is positioned in a flow path, the portion moving to control the flow through the member. Thus it is the porton itself which directly controls flow, being positioned in the path of flow.

This is distinct from known arrangements in which a shape memory element serves only as an actuator.

In the above described arrangement the opening through which flow takes place is in the member itself. Effectively, therefore, the flow cross-section of the slot defining the element will increase or decrease as the element moves. Indeed in an "open" condition the slot may be transformed to a different type of aperture. Whilst the portion could cooperate with another member to regulate flow, the above is the preferred arrangement and thus viewed from another aspect the invention provides flow control means comprising a member adapted to be positioned in a flow path, the member having therein an aperture into which extends a portion of the member, the portion being of a shape memory material and movable in response to a change in temperature, by means of a shape memory effect, so as to vary the flow cross-section of the aperture.

In general, the movement of the portion will be into or out of the plane of the aperture.

Flow control using a member in accordance with the invention could be in respect of liquids, gases or solids. The member could for example serve as a ventilator shutter for air or a screening device for solid, particulate material.

In the context of retaining or fastening, the portion will be e.g. in the form of a lug adapted to engage another member. It may move into engagement with the other member, thus exerting a clamping force or interlocking with part of the other member for example. In some circumstances it may be that no movement is required and in these cases it is the tendency to move which causes a clamping force.

Viewed from a still further aspect of the invention there is provided a member having thereon means for effecting attachment of the member to another member, such means comprising a portion of the member in the form of a lug of a shape memory material adapted to move or tend to move relative to adjacent parts of the member in response to a temperature change, by means of a shape memory effect, to engage the other member.

In the context of actuators, the invention permits a departure from, e.g. coil springs of shape memory alloy. Thus, for example, an actuator could be in the form of a replacement for a conventional diaphragm spring with radially directed elements, defined by e.g. slots, which change position.

Thus viewed from yet another aspect the invention provides an actuator in the form of a plate comprising a plurality of radially directed elements of a shape memory material arranged and adapted such that in response to a change in temperature the plate undergoes or tends to undergo a change in shape by means of a shape memory effect.

It will be appreciated that in the field of fastening, or of actuators, the primary function of the slot or other aperture will generally be to enable a lug, flap or the like to be formed from the material of the basic member, whereas in flow control the aperture normally has the function, generally in addition to defining the flap, of providing the flow path.Even in the field of actuators this may be desirable, with fluid flow through the apertures even if these are not intended to change in size.

In the preferred arrangements it is the provision of a flap lug or the like which enables greater versatility than previously possible.

The range of movement of e.g. a flow control flap can be made significant. Generally speaking the basic member will be in the form of a relatively thin sheet, plate, strip or the like.

- In general the basic member will be of a shape memory alloy and integral with the portion adapted to move or tend to move. For certain aspects of the invention it would though be possible for at least part of the member to be of another material such as a conventional alloy. Such a member could be provided with a number of openings over which are positioned shape memory flaps welded or otherwise secured to the basic member. It might be advantageous to have part of the flap of a shape memory alloy and part of another material, for example a hardened portion to dig into a member to be gripped, a resilient portion to effect a seal, or any other material as desired for particular applications. Where the element and the basic member are of the same material, at least in part, the element may be defined by one or more slots in the member, cut in a conventional way.A substantially regular array of slots and elements may be desirable for certain applications.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 comprises two perspective views of a first embodiment, at different temperatures; Figure 2 comprises a plan and a sectional view of a second embodiment; Figure 3 comprises a plan and a sectional view of a third embodiment; Figure 4 comprises a plan and a sectional view of a fourth embodiment; Figure 5 is a perspective view of a fifth embodiment; Figure 6 comprises a plan and a sectional view of a sixth embodiment; Figure 7 is a perspective view of a seventh embodiment; Figure 8 is a sectional and plan view of an eighth embodiment; Figure 9 is a diagrammatic view of a ninth embodiment; and Figure 10 is a sectional view of apparatus incorporating the embodiment of Fig. 8.

In Fig. 1 a plate of shape memory alloy 1 is shown having slot like openings 3 therein. At one temperature all plate portions 4 around and between parallel slot portions 3 extend in the same plane (see the left side of the figure). Thus between any two slots there can be considered to be defined an aperture which at this stage is covered by plate portions. At another temperature the strip like plate portions 4 between the slots 3 bulge out to a convex shape whereby the size and shape of the individual slots 3 changes to the configuration of openings 2 (see the right side of the figure). Thus the portions of the plate have moved out of the apertures previously defined.

The shape memory alloy plate 1 shown in Fig. 2 has a crenel shaped slot 3 cut therein delimiting two flaps 4 and 5. Due to suitable treatment of the flaps, they can bend outwardly at a certain temperature from their position in the plane of the plate 1 to a position shown in Fig. 2, thereby enlarging the size of the slots 3 to openings 2. Upon changing the temperature to its initial value, the flaps will return to their position extending in the plane of plate 1. Such a temperature change can e.g. be applied to the plate by a current of a fluid. A proper change in temperature of the fluid will then produce the desired deviation effect in the flaps. In principle, such a structure can be used as a ventilation shutter to regulate and control the evacuation of e.g. air through the openings 2 as a function of the air temperature.

A similar structure is shown in Fig. 3. Here however, the flaps 4 are covered with a layer 6 of flexible material containing a material able to heat the flaps by sending an electrical current therethrough. By heating the flaps 4, they can then change from a flat position to a curved position. An electrically insulating material will of course be interposed between the flaps 4 and the covering layer 6.

As shown in the embodiment of Fig. 4, a plurality of openings 2 with slot like portions 3 are provided preferably at regular intervals in a shape memory alloy plate 1 so as to produce a screening member with screening openings variable in size according to the temperature of the plate.

A further possibility as shown in Fig. 5 relates to the incision of loop like portions 4 in a shape memory alloy plate 1 as a means for fixing or anchoring the plate to a neighbouring or adjacent material 7. Such fixing is carried out by effecting a change in temperature.

It is also possible to cover a shape memory plate with e.g. an elastomeric layer 8 in the region of slots 3, as shown in Fig. 6. Thus, when the flap 4 extends in the plane of plate.

1 the slot 3 is covered and closed by an overlapping portion of the layer 8. By an apprpriate temperature change the closure of the slots 3 is interrupted due to the lifting of flap 4. Thus the layer 8 acts as a seal.

Another embodiment, shown in Fig. 7 relates to a tubular clamping member 9 with heat activatable flaps 4 which upon proper heating or cooling can exert a suitable radially oriented force on a member either inside or around the tube to provide a fixed connection therewith.

In the embodiments shown above, the openings enlarge in size and change e.g. from a slot like opening 3 in the plane of the plate to a wider opening with the flap 4 extending also in directions outside of the plane of the plate. However it is also possible to change the entire shape of the plate without, or only slightly, altering the size of the openings which remain in the plane of the surrounding plate. Such an embodiment is schematically shown in Fig. 8 wherein a circular flat disc 1 of shape memory alloy changes upon appropriate heating (or cooling) to a convex shape (approaching a part-spherical dome) shown in dotted lines. During this change in shape the slots 3 decrease in width but remain in the plane of the surrounding plate 1. A combination of both kinds of change in the slot shapes in one plate is of course conceivable.

Referring now to the embodiment of Fig. 9, there is shown a ventilating system for a motor vehicle radiator 10. The system comprises a shutter plate 11 of shape memory alloy with variable size openings, defined by flaps, in accordance with the invention. The plate 11 of zigzag shape is disposed between the radiator 10 and a fan 1 2. After starting the engine, water in the radiator warms up as well as the space 1 3 behind the radiator which is delimited by the shutter plate 11.

When the temperature in this space 1 3 rises sufficiently, e.g. to 55"C, rectangular flaps 14 in plate 11 start to bend rearwards so as to create openings in the shutter whereby the cooling air flow which traverses the radiator is allowed to pass through. This passage of cooling air is further intensified by the suction action of the rotating blades of fan 1 2. When the temperature of the air stream traversing the space 1 3 has lowered to a predetermined level, e.g. 45 to 50"C, the shutter plate flaps 14 are at a temperature where, due to their shape memory properties, they bend back to close the openings.From this point in time the cooling effect of the air is lowered so that the temperature in the radiator and in the space 1 3 again rises. When the temperature becomes again too high the flaps 14 are opened and the cooling cycle restarts. In this way it is possible to control the temperature of the radiator between substantially narrow limits. This is highly desirable for maximising the efficiency of the engine. The shutter 11 shall preferably have a zigzag shape as shown or an undulated shape, so as to increase its contact area with the air stream. The rectangular flaps 14 will be so arranged that the air flow can move in a substantially horizontal direction, thereby impinging frontally ontothe fan blades.

A similar shutter 1 5 can be placed in front of the radiator, however, with the flaps bending rearwards at about 5"C to allow cooling air to pass through the radiator. This is advantageous especially in cold weather conditions to speed up the heating of the radiator and so to minimise the period for bringing the engine to its operating temperature. In either case the back side of the flaps can optionally be covered with a flexible sealing strip 8 as suggested in the embodiment of Fig.6 so as to close the slot opening around the flap when it is in its closed position.

A zigzag or undulated shaped shutter plate of the type just described can also be used e.g. as a security device for fire hazards in warehouses where smoke ventilation systems are required. The shutter plate is then mounted in the roof of the room. When its temperature sufficiently rises due to fire and the development of smoke in the room then the flaps start to bend thereby creating evacuation openings for the smoke.

In the embodiment of Fig. 10, a temperature sensitive clutch device is illustrated for actuating a fan in response to the temperature of its environment. Temperature actuated fan systems are well known e.g. for use on truck engines to save energy and using a fluid coupling system. The present device comprises a rotating shaft 1 6 at whose end a shape memory actuator 1 7 is fixed by means of a clamping ring 1 8. The actuator 1 7 comprises a stack of slotted discs as illustrated in Fig. 8 and a bias disc-shaped belleville spring 26 having a number of openings 25 therein.

The slots 3 in the discs 1 7 are in alignment with each other to allow the air strem to pass through the stack. The outer circumferential edge of the disc 26 is fixed to a ring 1 9 with a conical outer surface. The fan blades 12 are mounted on the shaft 16 by means of member 21 and bearing 20. The member 21 is provided with a brake lining 22. When the temperature of the air stream (arrow 23) passing the fan is low, the actuator is in its convex shape. However, when the air temperature rises to a predetermined temperature (arrow 24), the actuator discs 1 7 will erect and push the ring 1 9 axially in the engagement with the brake lining 22 against the action of the bias spring 18. By this engagement, the member 21 and the fan blades 12 are coupled to the rotating shaft and thus start to rotate whereby evacuation of the hot air stream is intensified. Upon sufficient cooling of the airstream, the bias spring 18 pushes the discs 1 7 back to their convex shape. The member 21 and ring 19 disengage and the fan is no longer driven by the shaft 1 6.

Claims (14)

1. A member of a shape memory material having therein at least one slot defining, at least in part, a portion of the member adapted to move or tend to move in response to a change in temperature by means of a shape memory effect.

2. Flow control means comprising a member adapted to be positioned in a flow path, the member having therein an aperture into which extends a portion of the member, the portion being of a shape memory material and movable in response to a change in temperature by means of a shape memory effect so as to vary the flow cross-section of the aperture.

3. Flow control means as claimed in claim 2 wherein movement of the portion is into -and out of the plane of the aperture.

4. Flow control means as claimed in claim 3 wherein the movable portion is integral with the remainder of the member and defined by at least one slot therein.

5. Flow control means as claimed in claim 2, 3 or 4 wherein a pliable material is carried by the movable portion to act as a seal.

6. Flow control means as claimed in any of claims 2 to 5 wherein the movable portion is provided with heating means thereon.

7. Flow control means as claimed in any of claims 2 to 6 wherein a regular array of apertures and movable portions is provided.

8. Flow control means as claimed in any of claims 2 to 7 wherein the member is in the form of a sheet, plate, strip or the like.

9. Flow control means substantially as hereinbefore described with reference to Figs.

1; 2; 3; 4; 6 or 9 of the accompanying drawings.

10. A member having means thereon for effecting attachment of the member to another member, such means comprising a portion of the member in the form of a lug of a shape memory material adapted to move or tend to move relative to adjacent parts of the member in response to a temperature change, by means of a shape memory effect, to engage the other member.

11. A member as claimed in claim 10 wherein the lug is integral with the remainder of the member and defined by at least one slot therein.

1 2. A member as claimed in claim 10 or 11 in the form of a sheet, plate, strip or the like.

1 3. A member substantially as hereinbefore described with reference to Figs. 5 and 7 of the accompanying drawings.

14. An actuator in the form of a plate comprising a plurality of radially directed elements of a shape memory material arranged and adapted such that in response to a change in temperature the plate undergoes or tends to undergo a change in shape by means of a shape memory effect.

1 5. An actuator substantially as hereinbefore described with reference to Figs. 8 and 10 of the accompanying drawings.