GB1573204A

GB1573204A - Temperature responsive actuators

Info

Publication number: GB1573204A
Application number: GB19169/76A
Authority: GB
Original assignee: Delta Materials Research Ltd
Current assignee: Delta Materials Research Ltd
Priority date: 1976-05-10
Filing date: 1976-05-10
Publication date: 1980-08-20
Also published as: FR2351446A1; DE2720886A1; IT1083052B; FI771485A; DK203477A; NL7705175A; SE7705469L

Description

(54) TEMPERATURE RESPONSIVE ACTUATORS (71) We, DELTA MATERIALS RESEARCH LIMITED, a British Company of P.O. Box 22, Hadleigh Road, Ipswich, Suffolk IP2 OEG, 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 a temperatureresponsive actuator capable of performing an actuating function on change of temperature, for example to operate an indicator or to affect a control.

Such actuators are well known and usually take the form of bi-metallic elements, which change their shapes with change of temperature; the efforts exerted by a bimetallic element is limited. Actuators incorporating so-called "shape memory effect materials" have also been suggested. Thus, U.S. patent No. 3594674 describes the use of helical spring which is made of nickeltitanium shape memory alloy and which is arranged to operate electrical contacts when subject to temperature change.

A shape memory effect material as described in the above-mentioned U.S.

patent and as employed in the present invention has an elastic modulus which varies significantly with temperature in a reversible manner over a transition temperature range. In the case of an alloy, the variation of elastic modulus with temperature is associated with the martensitic transformation of the alloy, and accordingly the alloy is heat treated in known manner prior to use to bring it to a martensitic condition. The transition temperature range is dependent on the composition of the alloy and corresponds to the range through which the martensitic transformation takes place. Outside that range, change of temperature has little effect on elastic modulus until the temperature becomes so excessive that the martensitic condition is lost.

The actuators employing shape memory effect material and described in the abovementioned U.S. patent and elsewhere are responsive to the absolute temperature of the material and are incapable of responding to the difference in temperatures at two different locations. However, differential temperature actuators are frequently needed.

An object of the present invention is to provide an actuator which utilises shape memory effect materials and which responds only to differences in temperatures at different locations, but is substantially unresponsive to a change of temperature occurring at both locations.

The present invention provides a differential temperature detector which comprises first and second resilient members, each of which is secured to a relatively fixed element at one of two locations on the member, each of which is connected at the other of the locations to the other member with the members deformed in opposition, and each of which is made essentially of a shape memory effect material, whereby the position of said other location of either member is indicative of the difference in temperatures of the members.

The invention will be more readily understood by way of example from the following description of differential temperature actuator in accordance therewith reference being made to the accompanying drawings, in which Figure 1 shows a differential temperature actuator using leaf springs of shape memory effect alloy, Figure 2 is a graph explaining the operation of the actuator of Figure 1, Figure 3 shows an actuator using torsion tube springs, Figures 4 and 5 illustrate the use of the actuator of Figure 3 for operating a dis charge valve and a heat meter, respectively.

The actuator of Figure 1 consists of a pair of similar leaf springs 12 and 13 secured between two fixtures 14 and 15 with a fixed part of each engaging against a different one of the fixtures and the free ends 1 2A and 1 3A in engagement with one another to form an indicating finger. The leaf springs when locked as shown between the fixtures 14, 15 are elastically strained, having been deformed in opposition. the resulting stresses opposing one another. The leaf springs are made of the same shape memory effect alloy which is chosen to have a transition temperature range encompassing the range of ambient temperature to which the leaf springs are subject in use.

When the two leaf springs 12 and 13 are at the same temperature Tc, they are in the disposition shown with the indicating finger centrally between the fixtures 14 and 15. No change in position of the finger occurs if the two leaf springs change equally in temperature, since the elastic moduli of the two springs alter equally. If, on the other hand, the temperature of one only of the springs changes, one spring becomes stiffer than the other and the position of the finger at which the stresses of the springs are balanced is altered. The position of the finger is thus an indication of the difference in temperature of the two springs 12 and 13 and that finger is capable of exerting a controlling force as indicated by the arrows 16.

A biasing spring may be applied to the indicating finger as shown in Figure 1 at 17, that spring acting between the finger and an adjusting screw 18 threaded into the fixture 15. By operation of the screw 18, the bias applied can be varied; the adjustment enables the position of the indicating finger to be varied for zero temperature difference, and makes it possible to calibrate the actuator so that the finger reaches a given control position for a required temperature difference.

The operation of the actuator is explained by the diagram of Figure 2 where force applied by each of the springs 12, 13 is plotted against deflection of the spring from the unstressed condition. The force/deflection characteristics of spring 12 for different temperatures within the transition range are represented by the family of curves 20. the gradient of those curves increasing with temperature, i.e. the spring becomes stiffer with rise in temperature. The force/deflection characteristics of the spring 13 are represented by the similar family of curves 21.

The position of the indicating finger 12A, 1 3A is then represented by the intersection of the curve 20 pertaining to the temperature of spring 12 with the curve 21 pertaining to the temperature of spring 13.

When the springs 12, 13 are at the same temperature Tc, the Tc curves 20. 21 intersect at the point 22 and. generally, whatever is the actual temperature of the springs, the intersection point is on a vertical line 23 when there is no temperature difference. The indicating finger thus has a constant position represented by that line. If now the temperature of spring 13 is TC+AT, while spring 12 remains at temperature Tc, the indicating finger takes up a new position, at which the forces applied by the springs are balanced, and which is defined by the intersection of the curve 20 for temperature Tc with the curve 21 for temperature Tc + AT. i.e. at the point 24. If the indicating finger is subject to zero restraint, the finger moves to the position represented by the horizontal displacement of point 24 from line 23.However if the finger is constrained to a smaller displacement indicated by ex, the finger is capable of exerting a load represented by the vertical arrow 27 between the Tc line 20 and the Tc + AT line 21 at the displacement a.

Instead of the leaf springs 12, 13 other forms of springs may be used, as exemplified by Figure 3.

In Figure 3, opposed springs in the form of torsion tubes are utilised. Each tube 40 or 41 is held against movement at one end, and has clamped to its other end a radial arm 43 or 44. The axes of torsion tubes 40, 41 are parallel with the arms 43, 44 lying in the same plane. The arms are turned in opposite senses so as to stress the tubes oppositely and then locked together by connecting ends of the arms by a link 45 while the tubes are so stressed; link 45 is connected to the arms by pivot pins 46.

Tubes 40 and 41 are made of shape memory effect metal and have similar properties.

Accordingly the angular position of arm 43 remains fixed provided the temperatures of the tubes are the same. When there is a temperature difference, the torsional stiffnesses of the tubes are different, the stresses of the tubes are balanced at different angular dispositions of arms 43, 44 and link 43 takes up a position dependent on the temperature difference.

As in Figure 1, the actuator of Figure 3 can be calibrated by a calibrating screw 47 which acts on a spring 48 biasing the link 45.

The rigid link 45 of Figure 3 can be replaced by a flexible coupling. the use of which changes the temperature difference/position characteristic of the actuator.

The differential temperature actuators of this invention may be used simply to indicate temperature difference at two locations, or to operate a controlling or other mechanism. Two examples of the controlling function are illustrated in Figures 4 and 5.

Figure 4 shows a discharge valve, such as might be used in a waste heat recovery system. The valve is operated to dump a first liquid from its container when the temperature difference between that liquid and a second liquid falls below a given level. A differential temperature actuator similar to that of Figure 3 is employed, like reference numerals being applied to like parts. Torsion tube 40 is located in a container 50 for relatively hot liquid, while torsion tube 41 is disposed in a container 51 separated from container 50 by a partition 52 and containing relatively cold liquid. The ends of arms 43 and 44 are shown as entering slots in a horizontally guided cross-head 53. which is coupled by any suitable linkage represented by the line 54 to a valve member 55 receivable in a valve opening 56 in the bottom of container 50.

As in Figure 3, the cross-head 53 moves lengthwise according to the difference in temperatures of the liquids in containers 50 and 51. Provided that difference is greater than a prescribed value, the valve opening 56 remains closed by the valve member 55.

However. when the temperature difference falls below that value, the resulting movement of cross-head 53 causes, through linkage 54. the valve member 55 to be lifted out of opening 56 and the discharge of the liquid in container 50.

A heat meter is shown in Figure 5 utilising two linked torsion tubes 40. 41 similar to those of Figure 3. Those tubes 40 and 41 form part of the inlet and output pipework of a hot water heating system. the incoming hot water passing through torsion tube 40 and the outgoing cold water through torsion tube 41. Link 45 then takes up a position determined by the difference in temperature of the two water flows. A conventional flowmeter, represented by a rotor 60 in tube 40 coupled to control equipment 61, measures the flow of water in the system. Link 45 is coupled, through any suitable means represented by line 62. to control equipment 61 in which the measured flow and the measured temperature difference are multiplied, and the resulting rate of heat flow is integrated and displayed in a unit 62.

The temperature-responsive springs 12, 13; 30, 31; and 40. 41 are made of any shape memory effect alloy having the required properties.

WHAT WE CLAIM IS: 1. A differential temperature detector comprising first and second resilient members. each of which is secured to a relatively fixed element at one of two locations on the member, each of which is connected at the other of the locations to the other member with the members deformed in opposition, and each of which is made essentially of a shape memory effect material, whereby the position of said other location of either member is indicative of the difference in temperatures of the members.

2. A differential temperature detector as claimed in claim 1, in which each of the resilient members is a leaf spring, one end of one of the spring abutting against one end of the other said spring.

3. A differential temperature detector as claimed in claim 1, in which each of the resilient members is a stressed torsion tube, and in which the torsion tubes carry radial arms, which are connected together by coupling means retaining the tubes in torsional stress.

4. A differential temperature detector as claimed in claim 3, in which the coupling means are rigid.

5. A differential detector as claimed in claim 3, in which the coupling means are flexible.

6. Temperature responsive valve means comprising a differential temperature detector as claimed in any one of the preceding claims, a first container for a first liquid, the first resilient member being located in that first container, a second container for a second liquid, the second resilient member being located in the second container, a valve in one of said containers for discharging liquid therefrom. and a linkage between the coupling means and the valve, whereby the valve is opened when the temperature difference of the liquids falls below a given value.

7. A heat meter comprising a differential temperature detector as claimed in any one of the preceding claims, the first and second resilient members being in contact with a fluid at different temperatures, a flow meter for measuring the flow of that fluid, and computing means controlled by the coupling means and the flow meter to give an indication of heat transmitted.

8. A differential temperature detector, substantially as herein described with reference to Figures 1 to 3 of the accompanying drawings.

9. Temperature-responsive valve means, substantially as herein described with reference to Figure 4 of the accompanying drawings.

10. A heat meter, substantially as herein described with reference to Figure 5 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. might be used in a waste heat recovery system. The valve is operated to dump a first liquid from its container when the temperature difference between that liquid and a second liquid falls below a given level. A differential temperature actuator similar to that of Figure 3 is employed, like reference numerals being applied to like parts. Torsion tube 40 is located in a container 50 for relatively hot liquid, while torsion tube 41 is disposed in a container 51 separated from container 50 by a partition 52 and containing relatively cold liquid. The ends of arms 43 and 44 are shown as entering slots in a horizontally guided cross-head 53. which is coupled by any suitable linkage represented by the line 54 to a valve member 55 receivable in a valve opening 56 in the bottom of container 50. As in Figure 3, the cross-head 53 moves lengthwise according to the difference in temperatures of the liquids in containers 50 and 51. Provided that difference is greater than a prescribed value, the valve opening 56 remains closed by the valve member 55. However. when the temperature difference falls below that value, the resulting movement of cross-head 53 causes, through linkage 54. the valve member 55 to be lifted out of opening 56 and the discharge of the liquid in container 50. A heat meter is shown in Figure 5 utilising two linked torsion tubes 40. 41 similar to those of Figure 3. Those tubes 40 and 41 form part of the inlet and output pipework of a hot water heating system. the incoming hot water passing through torsion tube 40 and the outgoing cold water through torsion tube 41. Link 45 then takes up a position determined by the difference in temperature of the two water flows. A conventional flowmeter, represented by a rotor 60 in tube 40 coupled to control equipment 61, measures the flow of water in the system. Link 45 is coupled, through any suitable means represented by line 62. to control equipment 61 in which the measured flow and the measured temperature difference are multiplied, and the resulting rate of heat flow is integrated and displayed in a unit 62. The temperature-responsive springs 12, 13; 30, 31; and 40. 41 are made of any shape memory effect alloy having the required properties. WHAT WE CLAIM IS:

1. A differential temperature detector comprising first and second resilient members. each of which is secured to a relatively fixed element at one of two locations on the member, each of which is connected at the other of the locations to the other member with the members deformed in opposition, and each of which is made essentially of a shape memory effect material, whereby the position of said other location of either member is indicative of the difference in temperatures of the members.