WO2002013221A1

WO2002013221A1 - Electromechanical component

Info

Publication number: WO2002013221A1
Application number: PCT/DE2001/002883
Authority: WO
Inventors: Stefan Kautz; Hannes KÜHL
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-08-10
Filing date: 2001-07-30
Publication date: 2002-02-14
Also published as: DE10039203A1; DE10039203C2

Abstract

The invention relates to an electromechanical component comprising at least one actuator consisting of a shape memory alloy. Said actuator alters shape upon reaching a certain temperature and moves into a final position. The displacement path of the actuator is restricted in such a way that it does not reach said final position.

Description

description

Electromechanical component

The invention relates to an electromechanical component with at least one actuator made of a shape memory alloy, which changes its shape when a certain temperature is reached and moves into an end position.

Such an electromechanical component is implemented, for example, in the form of an isolating switch device. This isolating switch device is used to open a circuit closed via it very quickly in the event of a fault and thus to be able to interrupt it in order to prevent interference-related overvoltages or the like from reaching the

Applied circuit equipment affect and this can be damaged or destroyed. To quickly open the circuit, such isolating switch devices use an actuator made of a shape memory alloy. These actuators are often also called SMA actuators (shape memory alloy actuators). Such actuators are characterized by the fact that they can change shape depending on their temperature. This is achieved by applying a preferred direction to them by means of suitable form annealing, in which the grains preferentially align themselves during the temperature-related phase change. One-way actuators are known which, when the temperature rises from a certain transition temperature, change from the shape of the cold state to another, which occurs due to the phase change from martensite to austenite and the grain growth in the direction of the preferred direction. After it has cooled again, the actuator remains in the form it was in, ie it does not change its shape back. This is the case with so-called single-gate actuators. Two-way actuators automatically change their shape between "cold" and "warm" states. When used, for example, in a disconnector device, one-way actuators are frequently used, which are coupled, for example, with a spring element, for example a spring clip. The circuit is closed via the spring clip. The actuator is arranged in such a way that it is bent by the spring clip, for example from the horizontal position. The horizontal position corresponds to the stamped high temperature shape. If the circuit has to be opened due to a malfunction, the actuator is briefly warmed up above the transition temperature so that it converts to the horizontal or elongated form and thereby entrains the spring clip.

It is disadvantageous, however, that the known actuators show a significant aging or fatigue effect, for example in the case of switch use with cyclical actuator use, in such a way that the actuating or movement path of the actuator is significantly shortened. This means that the actuator travel decreases significantly as the number of cycles increases.At the same time, a sifting of the travel in the direction of a restoring force can be observed - in the case of the one-way actuator of the shape described above, for example, the spring clip. This means that the actuator can be deflected further by the applied force, the older it is or the more often it has been actuated. As a result, the actuator no longer reaches the “maximum” end position impressed due to the original shape annealing with increasing working time, and the shaping behavior also changes.

This fatigue effect is known. In order to compensate for it to some extent, such actuators are "pre-aged" or many cycles are run before they are actually used in order to artificially reduce the travel. This is very complex and cost-intensive. Furthermore, the compensation is carried out by means of a corresponding system design, that is to say dimensionally and dimensioned accordingly the components or the distances.

The invention is therefore based on the problem of an electromechanical one. Component with an actuator from a molded to specify memory adjustment in which the aging effect can be largely suppressed without carrying out upstream steps to compensate for the fatigue effect.

To solve this problem, it is provided according to the invention in an electro-mechanical component of the type mentioned at the outset that the movement path of the actuator is limited in such a way that it does not reach the end position.

It has been found that the fatigue effect can be adequately suppressed if the movement of the actuator during the shape conversion is so limited that it cannot assume the "maximum" end position due to the conversion. As part of the manufacture of an actuator, a shape annealing step is carried out as described During this shape annealing, a preferred direction is embossed, in which the grains grow during the transformation into the other phase, ie during the martensite-austenite transformation. When the transformation is completely completed, the actuator reaches its transformation-related maximum end position. According to the invention, this is the case but now prevents what, as has been proven in elaborate tests, leads to the fact that the travel defined between the one position from which the actuator moves when the shape changes, due to the movement limitation, does not change into the movement-limited position even with high number of cycles. It is believed that s The fatigue suppression is caused by the fact that, due to the travel path limitation, the conversion to the other phase or the grain alignment does not take place completely, although the given temperature would actually require this. As a result, due to the limitation of the travel range, the actuator is subject to a continuous voltage. This means that the preferred direction cannot be "broken down" or "dissolved", which is presumably the basis of the fatigue-related shortening of the supporting leg when the material can change shape without restriction. As a result of this travel path limitation according to the invention, it is achieved that the actuator can always run through the limitation-related maximum movement path since, as stated, it does not tire, which is why, on the one hand, permanent functional reliability is achieved and, on the other hand, the complex compensation methods upstream of the use of the component can be omitted.

According to a first alternative of the invention it can be provided that at least the movement path which the actuator performs as a result of a temperature increase when the specific temperature is reached is limited. This is the normal case of a one-way design of the actuator, as described at the beginning, where the actuator changes its shape, for example, when its temperature is increased in a targeted manner by current applied to the actuator.

In contrast, an alternative provides that at least the movement path which the actuator performs as a result of a temperature drop when the specific temperature is reached is limited. Components of this type are designed, for example, for use in hot environments and react to a sudden cooling down by a corresponding change in shape. So there is a travel limit to the cold side.

It is of course expedient if both movement paths are limited, which is expedient in the case of a two-way design of the actuator. With such an actuator, two preferred directions are embossed, which the actuator takes depending on the temperature present. If it is heated, it changes its shape according to the preferred direction intended for the hot state; if it cools down again, the shape automatically changes back according to the preferred direction impressed in the cold state. In order to suppress the fatigue effect, it is already sufficient if the movement path is limited or shortened by a very short distance, ie if the actuator is under very low voltage due to the path limitation. The movement path can expediently be limited by at least 5%, in particular by at least 10% of the total distance between the starting position and the end position, which the actuator would assume without restriction.

As described, the actuator can be a one-way actuator, which is pushed, for example, via a spring element into a first position, from which it moves when the elevated temperature is reached. For example, a spring clip or a spiral spring that acts directly or indirectly on the actuator can be used as the spring element. Already at this point it should be pointed out that the specific design or conception of the component with regard to the actuator arrangement and the other parts do not play a role for the effect that occurs, namely the suppression of fatigue, as long as the travel path limitation according to the invention is implemented. This means that an electromechanical component according to the invention can be constructed in any shape as long as the movement path is limited according to the invention. This also applies to components in which a two-way actuator is provided as the actuator.

In general, the actuator can be designed as a strip, as a wire or as a spring, in particular as a spiral spring. With each of these design variants, the objective according to the invention is achieved with a corresponding limitation of travel.

Further advantages, features and details of the invention result from the exemplary embodiments described below and from the drawings. Show: 1 is a schematic diagram of an electromechanical component according to the invention with a one-way actuator with travel range limitation,

2 shows a schematic diagram of the component from FIG. 1 without path limitation,

3 is a schematic diagram to illustrate the path limitation of a two-way actuator designed as a bending strip,

4 shows a schematic diagram to illustrate the travel limitation of a two-way actuator designed as a spiral spring,

5 is a schematic diagram to illustrate the path limitation of a one-way actuator designed as a wire,

FIG. 6 shows a course diagram of the travel of a one-way actuator of a component according to FIG. 1 with no travel restriction with an actuator made of a CuAlNi alloy, FIG.

7 shows a course diagram of the travel of the actuator from FIG. 6 with travel limitation.

8 shows a course diagram of the travel of a further actuator made of a CuAlNi alloy,

9 is a flow chart of the travel of the actuator from FIG. 8 with travel limitation.

FIG. 10 shows a course diagram of the travel of a one-way actuator of a component according to FIG. 1 without travel restriction with an actuator made of a NiTi

Alloy, FIG. 11 shows a course diagram of the travel of the actuator from FIG. 10 with travel limitation.

In the case of the component indicated in FIG. 1, an embodiment of a known disconnector device is assumed. Fig. 1 shows this only schematically in the form of a schematic diagram, since the precise structure of a disconnector device is not important for the actual operating principle. As a result, only the elements central to the invention are shown in FIG. 1. The electromechanical component 1 shown in FIG. 1 comprises an actuator 2 made of a shape memory alloy, which in the example shown is designed as a bending strip and is fixed at one end via a fastening 3. The other end interacts with a spring element 4 in the form of a spring clip, which is rotatable about the axis 5. This spring clip also represents a contact clip that bears against a circuit contact 6 in the extended position in FIG. 1. In this state, a circuit in which the component 1 is integrated is closed. The extended position is the normal one

Position when there is no fault. Due to the spring action of the spring element 4, the actuator 2 is stretched into the bent position. This means that the spring force of the spring element 4 is greater than the restoring force of the actuator in the cold state.

In the event of a fault, it is now necessary to break the contact between the spring element 4 and the switching contact 6 as quickly as possible. In this case, the actuator 2 is energized so that it heats up and - since it consists of a shape memory alloy - it changes its shape. This is indicated in FIG. 1 from the normal position according to reference symbol A by the position marked with B. The spring element 4 designed as a spring clip is pivoted about the pivot axis 5 and guided out of its contact with the contact 6. However, the movement path of the actuator 2 is limited by a path limiting part 7. In the normal case, the actuator would assume the horizontal or elongated position marked C in FIG. 2, which reflects the prior art. He takes this when the temperature-related phase change can take place completely and his path is not limited. According to the invention, however, see FIG. 1, the movement path is limited in such a way that this end position C is not assumed. This probably leads to the fact that the phase change cannot take place completely, although the elevated temperature would require this. Due to the travel limitation, the actuator remains in position B in a pretensioned state, which prevents the preferred position from being released, which is presumably the cause of aging.

3 shows an electromechanical component with a two-way actuator 8 made of a shape memory alloy. Depending on the temperature, it changes its shape in both directions, the maximum end positions being shown by the dashed lines. The travel path between these end positions is now limited twice, that is to say in each direction by means of the travel limitation part 9a, 9b.

Fig. 4 shows in the form of a schematic diagram the principle of operation in a two-way actuator in the form of a spiral spring 10. The upper illustration shows the spring in an impressed high temperature form, the representation below shows the spring in an impressed low temperature form. According to the invention, the respective path of the spring is now impeded, for example when this spiral spring 10 is used in a disconnecting switching element, which is shown in the lower two representations. On the one hand, the path limitation of the expanding spring is shown (FIG. 4C), which is indicated by the dashed line 11. The spring cannot therefore extend into the axial end position shown in FIG. 4A. The same applies to the movement path of the spring at low temperature. There, too, see FIG. 4D, the path through a disability (dashed line 11), so that the spring cannot contract into the minimum end position shown in FIG. 4B.

Fig. 5 shows an actuator 12 in the form of a wire, which is designed as a one-way actuator. The upper illustration (FIG. 5A) shows the actuator 12 in the extended or longest end position, which it assumes at a low temperature, for example room temperature. FIG. 5B below shows the shortened actuator 12 at a higher temperature. Finally, the path obstruction of the actuator 12 is shown in FIG. 5C (dashed line 13), which prevents the elongated, cold actuator 12 from contracting completely when it is brought to a high temperature in the event of a fault and which is shown in FIG. 5B could assume the end position shown. This path is limited in order to achieve the advantages mentioned at the beginning.

Practically all shape memory alloys can be used for an actuator. Ti-Ni are particularly suitable

Alloys. So go z. B. from "Materials Science and Engineering", Vol. A 202, 1995, pages 148 to 156 differently composed Ti-Ni and Ti-Ni-Cu alloys. In "Intermetallic", Vol. 3, 1995, pages 35 to 46 and "Scripta METALLURGICA et MATERIALIA", vol. 27, 1992, pages 1097 to 1102, various Ti ₅₀ Ni ₅ o-χPd _x shape memory alloys are described. Instead of the Ti-Ni alloys, of course, other shape memory alloys are also described For example, Cu-Al shape memory alloys are suitable. A corresponding Cu-Zn24Al3 alloy can be found in "Z. Metallkde.", Vol. 79, H. 10, 1988, pages 678 to 683. A further Cu-Al-Ni shape memory alloy is described in “Scripta Materia- lia”, Vol. 34, No. 2, 1996, pages 255 to 260. Of course, other alloy partners can be added to the aforementioned binary or ternary alloys such as, for example, alloyed with HF. 6 and 7 show a first test example with a one-way actuator made of a CuA113Ni4 alloy. This actuator was bent from its straight position with a load of 300 g, the maximum deflection path being limited by means of a stop. This deflection position lies at the zero point of the ordinate. The conversion-related deflection of the actuator is plotted along the ordinate and the time in minutes along the abscissa. A total of 1900 deflection cycles, in which the actuator was briefly energized from the "bent" position and thus warmed up so that it changes shape, after which it cools down again, were examined over a test period of 3800 minutes. The actuator was also examined within one cycle 17A, the rows of dots show the actuation path covered within an investigated deflection cycle.

The deflection at the start of the experiment is evidently approx. 5 mm. The maximum deflection, however, clearly decreases with increasing test duration due to the aging effect. At the end of the experiment, the deflection was approx. 2 mm. The travel range therefore decreased by around 60%.

This contrasts with the course of the experiment, as shown in FIG. 7. There too, a CuAll3Ni4 actuator was investigated as a one-way actuator, which was also deflected with a load of 300 g and was energized with 17 A within a cycle. During the test period of 3800 minutes, 1850 cycles were examined here. In contrast to the previous experiment, however, the shape-related movement path of the actuator was limited by a stop at 3.8 mm in the case of a shape change due to temperature increase. Obviously the actuator reaches the stop continuously over the entire duration of the test. In this experiment, the actuator could not, as in the experiment shown in FIG. 6, extend indefinitely to the maximum possible end position, but the movement path was limited to what leads to the actuator being continuously under a certain minimum voltage, which counteracted fatigue.

FIGS. 8 and 9 show a similar one-way actuator made of CuAll3Ni4, which according to the test according to FIG. 8 was operated with 400 cycles within a test period of 800 minutes. The actuator was also energized with 17A, but the deflection weight was only 150 g. In this example, the load-related deflection path, which actually lies at the zero point of the ordinate, was not limited there.

The result obtained corresponds to that shown in FIG. 6. Here, too, it can clearly be seen that the path of movement becomes ever shorter when energized. If the path of movement is still around 9 mm at the start, the actuator is only deflected by a little more than 5 mm towards the end of the test. It is also striking that there is no impediment to the load-related deflection, which is noticeable in the fact that the starting points of the respective lines drift below the zero point. Ultimately, this is also related to fatigue.

Such a fatigue effect does not occur here according to FIG. 9 if the movement path caused by the conversion is limited. In the experiment according to FIG. 9, this path was limited at 6 mm by means of a stop, and the load-related deflection was also limited here at the zero point. Obviously, the deflection over the test duration (here 1000 minutes with 495 cycles with a current supply of 17A) does not change over the entire test duration, i.e. the actuator always reaches the stop at 6 mm.

10 and 11 finally show the corresponding tests with a NiTi (50:50) actuator, which was also operated here as a one-way actuator. This was bent with a load of 200 g. The test time was 3800 minutes with 1900 cycles. Obviously, see Fig. 10, also here Deflection very clearly from a maximum at 8.4 mm to a minimum of approx. 3 mm.

According to FIG. 11, however, the change in movement path was limited by means of a stop at 5.7 mm. This stop was achieved over the entire test period within each cycle, which shows that the aging effect can also be suppressed with this actuator.

Claims

claims

1. Electromechanical component with at least one actuator made of a shape memory alloy, which changes its shape when it reaches a certain temperature and moves into an end position, since you rch noted that the movement path of the actuator (2, 8, 10, 12) is limited is that it does not reach the end position (C).

2. Electromechanical component according to claim 1, so that at least the movement path which the actuator (2, 8, 10, 12) performs as a result of a temperature increase when the specific temperature is reached is limited.

3. Electromechanical component according to claim 1, so that at least the movement path that the actuator (2, 8, 10, 12) performs as a result of a temperature drop when the specific temperature is reached is limited.

4. Electromechanical component according to claim 2 and 3, so that both paths of movement are limited.

5. Electromechanical component according to one of the preceding claims, that the movement path is limited by at least 5%, in particular by at least 10% of the total distance between the starting position and the end position.

6. Electromechanical component according to one of the preceding claims, characterized in that the actuator (2, 12) is a one-way actuator.

7. Electromechanical component according to claim 6, so that the actuator (2) is pushed via a spring element (4) into a first position from which it moves when the temperature is reached.

8. Electromechanical component according to one of claims 1 to 5, d a d u r c h g e k e n n z e i c h n e t that the actuator (8, 10) is a two-way actuator.

9. Electromechanical component according to one of the preceding claims, that the actuator (2, 8, 10, 12) is a strip, a wire or a spring, in particular a spiral spring.