EP0013280A1 - Selectively acting thermal circuit breaker, method for its release and its use for electrical protection - Google Patents

Abstract

1. Thermal switch with a selective action, possessing a switching element (18) which is made from an alloy having a shape-memorising capability and which is located, at least at a first point (15), in a manner essentially permitting free movement, and is rigidly attached to a body (16), characterised in that the mass (m) of this body (16) is adjustable and is assigned to a limiting acceleration-value (xG ) for triggering this thermal switch, it bein possible to preset this limitting acceleration-value.

Description

The invention relates to a thermal switch and a method for triggering a switching operation using a Tharmo switch according to the preamble of claims 1 and 6.

Secured thermal switches, e.g. Bimetallic strips, fuses or control valves with thermocouples trigger a switching process when a specified temperature value is exceeded with a relatively large time delay. Thermal switches are usually used to interrupt an electrical circuit.

The incorrect voltage and its duration, amplitude increase and repetition are of particular importance for the operational safety of electrical devices and systems. Via the electrical distribution network, interference voltages in devices and systems can lead to malfunctions or destruction of semiconductors in sensitive electronic circuits, to malfunctions in control systems, to loss of information or to flashovers due to poor insulation or too small creepage or clearance distances, switches with a large time delay are unsuitable for protecting such devices. Bimetallic strips also show signs of fatigue after longer use, which lead to a change in the response temperature.

Thermal switch with a relatively small switching delay using one of the caltutra gear Solving element made of a shape memory alloy are known, inter alia, from DE-OS 2 026 629, 2 139 852 and 2 701 884. The relatively large change in shape of this switching element when the temperature rises above the initial temperature of the phase transition from the low to the high temperature phase of the shape memory alloy is used to actuate a switch. The switching element can be flowed through and heated directly by the current to be switched. The heating can also be carried out by a heater inserted into the circuit. From DE-OS 2 701 884 it is known to interrupt the current in the circuit when a certain maximum current value is exceeded. One problem with the design of switches, in particular for line and overcurrent protection, is to ensure good selectivity in the switching conditions, i.e. the switch should only open after a current tolerance value has been reached when a predeterminable current rise is exceeded and not with all overcurrents.

The object of the invention is to ensure the triggering of a switching process with high selectivity of the switching condition.

The object is achieved according to the characterizing part of claims 1 and 6. Developments of the invention are described in the subclaims.

The invention is based on the new knowledge of the kinetics of the shape memory effect. An advantage of the invention is that the switching process selectively relates to the initial value, caused by an overcurrent, of a temporal change in the temperature in the switching element and is not in terms of the transmitted energy. The pretension applied to the switching element by a tensioning device can be adjusted so that the switching element can be deformed after cooling through under critical overcurrent.

• Fig. 1 das Prinzip des Formgedächtniseffektes,
  • a) den Einwegeffekt,
  • b) den Zweiwegeffekt,
• Fig. 2 die Dehnung als Funktion der Temperatur,
  • a) für den Einwegeffekt,
  • b) für den Zweiwegeffekt,
• Fig. 3 das Schema eines einfachen Thermoschalters in einer auch für Prüfzwecke geeigneten Ausführungsform,
• Fig. 4 die chemische Energie G der zwei Phasen Martensit und Austenit einer Formgedächtnislegierung als Funktion der Temperatur T (schematisch),
• Fig. 5 den prozentualen Anteil des Martensits M als Funktion der Temperatur T,
• Fig. 6 den elektrischen Widerstand R einer Formgedächtnislegierung (a) vor und (b) nach einem Aufheizen als Funktion der Zeit t,
• Fig. 7 das Schema eines mechanischen Modells aus einer Feder K, einer Stossdämpfungseinrichtung mit einer Dämpfungskonstante α und einer Masse m,
• Fig. 8a, 8b, 8c eine halbschematische Darstellung eines Thermoschalters in einem thermoelektrischen Schalter mit Zusatzsicherungselement und mechanischer Schaltverstärkung in verschiedenen Stellungen und
• Fig. 9 ein Funktionsschaltbild des Thermoschalters.

The invention is described below using exemplary embodiments. Show it:

• 1 shows the principle of the shape memory effect,
  • a) the one-way effect,
  • b) the two-way effect,
• 2 shows the strain as a function of temperature,
  • a) for the one-way effect,
  • b) for the two-way effect,
• 3 shows the diagram of a simple thermal switch in an embodiment which is also suitable for testing purposes,
• 4 the chemical energy G of the two phases martensite and austenite of a shape memory alloy as a function of the temperature T (schematic),
• 5 shows the percentage of martensite M as a function of temperature T,
• 6 shows the electrical resistance R of a shape memory alloy (a) before and (b) after heating up as a function of time t,
• Fig. 7 shows the schematic of a mechanical model from a Spring K, a shock absorption device with a damping constant α and a mass m,
• Fig. 8a, 8b, 8c is a semi-schematic representation of a thermal switch in a thermoelectric switch with additional fuse element and mechanical switching amplification in different positions and
• Fig. 9 is a functional circuit diagram of the thermal switch.

Fig. La) shows the one-way and Fig. 1b) the two-way shape memory effect. These effects occur with shape memory alloys, ie with thermoelastic martensite, which, after a so-called pseudo-plastic deformation at low temperature, return to their original shape when they are heated above a critical temperature. These alloys exist in a martensitic low-temperature phase lower, face-centered orthorhombic or monoclinic symmetry and in an austenitic high-temperature phase high, cubic body-centered symmetry. In the martensite phase there are no platelets or lamellae with different crystallographic orientations. At a high temperature of, for example, 600 ° C., the alloy is brought into a desired, for example elongated, rod shape and annealed. During cooling, when a critical temperature is exceeded, the austenitic phase changes into the martensitic phase. If at a low temperature T ₁ is now deformed, for example bent, stress-induced or reoriented martensite formation results in a quasi-stable shape which bears the original straight structure. When heating above a temperature T ₂ , which is above a critical temperature, a straight structure spontaneously arises again from the curved effect with the one-way effect. At
subsequent cooling no longer takes place spontaneously. However, if the alloy is deformed again at temperature T ₁ , the described effect is repeated when heating to T ₂ .

With the two-way effect, a body deformed, for example bent, from a shape memory alloy at temperature T spontaneously only partially returns to its original shape when heated to temperature T ₂ . When it subsequently cools down to T _{1, it} deforms again spontaneously, but not to the degree of deformation applied from the outside. The two temperature-induced, spontaneous changes in shape can be repeated in successive temperature cycles between T ₁ and T ₂ .

Fig. 2 shows another representation of the memory effects. Depending on the alloy composition, strains or pseudo-plastic deformations up to about 8% can be recovered for the one-way effect shown in FIG. 2a, while strains or deformations of up to 1.5% for the two-way effect shown in FIG. 2b. are known. While the deformation in the one-way effect drops to zero due to heating and retains this regressed shape when it cools, a deformation of about 2% remains in the two-way effect. When cooling below a certain temperature, a spontaneous deformation of about 1.5% occurs, which spontaneously regresses when the alloy is heated.

• a) durch eine irreversible plastische Verformung über den pseudo-plastischen Bereich der Legierung hinaus, d.h. von mehr als etwa 8 %,oder
• b) durch eine Temperaturerhöhung um etwa 50 K über die Endtemperatur der Austenitumwandlung hergestellt werden.

The two-way effect can be created by creating dislocations and lattice defects, for example

• a) by an irreversible plastic deformation beyond the pseudo-plastic area of the alloy, ie more than about 8%, or
• b) are produced by increasing the temperature by about 50 K above the final temperature of the austenite transformation.

The part of the deformation leading to dislocations is not recovered during heating. When it cools down again, the residual stress field of the lattice defects favors the regression of martensite orientations, which were generated by the originally applied stress, and leads to a smaller change in shape in the direction of the original deformation when it cools down. A small two-way effect is generated in subsequent thermal cycles.

If a tension is exerted on a shape memory alloy, the temperature range of the phase transition shifts to higher temperatures, as indicated by the broken line in FIG. 2a. Depending on the alloy composition, the conversion from the low to the high temperature phase can be between approximately -180 ° C and +250 ° C.

4 shows the chemical energy G of the martensite and austenite phase as a function of the temperature T. At low temperatures, martensite has less energy than austenite. Above a temperature T ₀ , at which both phases are in thermodynamic equilibrium and have the same chemical energy G, austenite has a lower energy than martensite.

If austenite is to be converted into martensite by cooling, the shape memory alloy must be cooled below T, as shown in FIG. 5, since elastic or nucleation energy must be supplied because of the volume.

At a _Mar t _ens it _umwandlun g-start temperature T _MS conversion starts at a Martensitumwandlungs-Endzemperatur T _MF it is completed, that is, there remains no austenite. Even at temperatures above T _MS , however, a voltage applied from the outside can make a chemical energy contribution to the nucleation or to the martensite, ie a voltage-induced martensite can be generated. If a body made of a shape memory alloy is first cooled below T _MS or T _MF and then deformed, a reorientation of the martensite platelets is produced, among other things, by means of a twin shearing process, which leads to a reversion of the deformation when heated.

The conversion of martensite to austenite begins at a so-called critical temperature T _AS above T ₀ and ends at a temperature T _AF .

In order to be able to produce a large shape memory effect, the volume change caused by the phase transition must be small, since otherwise many dislocations are generated in order to adapt the volume differences. Due to an increased dislocation density, the martensite is solidified or hardened and a reorientation due to an applied tension is no longer possible, as is the case with steel. The most important property of a shape memory alloy for an application as a switching element is that in the Conversion of the deformation when heating up work or tension can be generated. An energy density of 2 MJ / m ³ can be achieved for Ni-Ti base alloys, which is significantly higher than that of bimetal. By hindering the change in shape during heating, stresses of more than 650 MPa can be generated. The achievable force and the path depend on the sample geometry. In the case of a round bar, the length of which is 10 times its diameter, the bending force is 20 times less than the tensile force, but the displacement of the free end in the case of bending is 10 times the displacement in the event of tensile stress.

mit der Anfangsbedingung:

wobei xmax die maximale Dehnung bedeutet, die durch Aufheizen eines Federkörpers als Ergebnis eines Formgedächtniseffektes erreichbar ist. Unter diesen Voraussetzungen hat die Differentialgleichung (1) die Lösung:

mit

stellt die elastische Energie der Feder dar, die beim Aufheizen in eine Gestaltänderung innerhalb einer charakteristischen Bewegungszeit

mit einer wirksam werdenden Kraft F umgesetzt wird.6, curve a shows the resistance R of a wire made of a mechanically loaded or prestressed shape memory alloy before heating up as a function of time t. Curve b was generated by sending a short-term current pulse from a capacitor discharge (875 V, 25 µ F) through this wire and thereby heating it up. The resistance characterizes the structure or the phase transition of the alloy. The movement of the wire corresponding to the measured resistance vibration is explained using a mechanical model shown in FIG. 7, in which K is the spring constant of a spring, m is a mass, the damping constant, x the path. or a deflection, x or x mean the first or second derivative of the path according to time and g the acceleration due to gravity. The differential equation applies to this model:

with the initial condition:

where xmax means the maximum elongation that can be achieved by heating a spring body as a result of a shape memory effect. Under these conditions, the differential equation (1) has the solution:

With

represents the elastic energy of the spring, which when heated into a shape change within a characteristic movement time

with an effective force F is implemented.

mit

• q Querschnittsfläche des Formgedächtniskörpers
• 1 Länge
• d relative Dichte
• C spezifische Wärmekapazität
• Δs spezifische Entropie
• Δh spezifische Enthalpie
• C spezifische Wärmekapazität
• ε_d durch Verformung aufgebrachte relative Formänderung und
• ε_M maximale relative Formänderung durch Phasenumwandlung.

The spring constant K depends on the type of movement, such as tension, bending, etc., on the type of shape memory alloy and on the size of a mechanical preload. Without preload, K for tension or compression results in:

With

• q cross-sectional area of the shape memory body
• 1 length
• d relative density
• C specific heat capacity
• Δs specific entropy
• Δh specific enthalpy
• C specific heat capacity
• ε _d relative shape change caused by deformation and
• ε _M maximum relative shape change due to phase transformation.

wobei V das Volumen des Körpers bedeutet.If a body or wire made of a shape memory alloy is heated by an electrical current I flowing through it, the relationship applies to temporal temperature changes dT / dt in a temperature range in which there is no shape change caused by a shape memory effect.

where V is the volume of the body.

wobei σ₀ eine Material konstante ist. Diese Spannung σ wird in den in den Fig. 3 und 8a, Bezugsziffer 38, dargestellten Thermoschaltern zur Auslösung eines Schaltvorganges benutzt.Above the critical temperature T _AS for the recovery, a mechanical stress σ proportional to T - T _AS arises in the shape memory body _:

where σ _{0 is} a material constant. This voltage σ is used in the thermal switches shown in FIGS. 3 and 8a, reference number 38, to trigger a switching operation.

The principle of the thermal switch is based on FIG. 9 purifies. Any time-dependent physical quantity f (t), which should trigger a switching process or provide a switching signal y ₁ when a predefinable condition, for example when a certain limit value is exceeded, is assigned in a converter 41 to one of these input quantities f (t) time-dependent heat or thermal energy Q (t) is transformed if it is not already specified as heat. This heat Q (t) is transformed in a further converter 42 into an acceleration x, which is compared to a comparator 43 with an acceleration limit value x _G. For x> x _G , the switching signal y ₁ is present at the output y of the comparator 43, otherwise the signal y ₂ . Synonymous with these signals y ₁ or y ₂ , which are dependent on the output of the comparison, is an “on” or “off” or a “changeover” of a switch.

in Wärme, diese gemäss Gleichung (11) in mechanische Spannung und diese gemäss_den Gleichungen (7) und (1) in Kraft F bzw. Beschleunigung x transformiert. Der Vergleicher 43 wird durch eine einstellbare Masse 16 dargestellt, wobei die Trägheit dieser Masse zur Realisierung des Beschleunigungsgrenzwertes x_G verwendet wird. Erst wenn eine durch'den Formgedëchwriseffent beim Aufheizen des Schaltelementes erzeugue Kraftwirkung bzw. Beschleunigung x' diesen vorgeb- baren Brenwer überschreitet, erfolgt eine Auslösung des Schaltsignals bzw. ein Schaltvorgang. Largsam verlaufende Strom- bzw Temperaturänderungen in Schaltelement 18 lösen somit keinen Schaltvorgang aus. Ebenso lösende Stromänderungen, die Temperaturänderungen ausserhalb der Phasenübergänge zwischen T_AS und T_AF bzw. zwischen T_MS und T_MF entsprechen, keine Schaltsignale aus. Es handelt sich so- 'mit um einen selektiy wirkenden Thermoschalter, der unter anderem für ein schnelles Abschalten von Ueberströmen geeignet ist. Dafür wird der Phasenübergang von Martensit in Austenit entsprechend dem Temperaturbereich von T_AS bis T_AF verwendet Dieser Schaltbereich ist durch Dimensionierung des Schaltelements, Zusammensetzung der Legierung und mechanische Vorspannung einstellbar.3 and 8a, reference number 38, the time-dependent physical quantity f (t) is an electrical current I (t). The converters 41 and 42 are formed by the switching element 18 from a shape memory alloy. The electrical current I (t) is in accordance with this switching element

, x transformed into heat according to this equation (11) in tension, and this according to _d s equations (7) and (1) in the force F and acceleration. The comparator 43 is represented by an adjustable mass 16, the inertia of this mass being used to implement the acceleration limit value x _G. Only when one is through Formgedëchwriseffent when heating the switching element generate force or acceleration x 'exceeds this predetermined Brenwer, the switching signal is triggered or a switching process. Largely running current or temperature changes in switching element 18 thus do not trigger a switching process. Current changes, which also correspond to changes in temperature outside the phase transitions between T _AS and T _AF or between T _MS and T _MF , do not trigger any switching signals. It is thus a 'selectively acting thermal switch which, among other things, is suitable for quickly switching off overcurrents. The phase transition from martensite to austenite corresponding to the temperature range from T _AS to T _{AF is} used for this. This switching range can be adjusted by dimensioning the switching element, composition of the alloy and mechanical preload.

innerhalb eines Zeitintervalles mit 4t = 2 ms den Wert von SZ = ₁₀₀₀ A²s, so zerreisst das Schaltelement 18 und unterbricht den Stromkreis, wie in Fig. 3b dargestellt. Das Schaltelement wirkt hierbei als elektrische Sicherung mit einstellbarer Empfindlichkeit. Wenn der Stromanstieg schneller als ein vorgebbarer Wert ist, überschreitet die mechanische Spannung σ die Zerreisspannung des Schaltelementes bevor sich die Masse 16 zu bewegen beginnt. Die Anfangsgestalt des Schaltelementes ist so gewählt, dass der Abstand zwischen den Bruchstücken nach dem Zerreissen gross genug ist, um eine Trennung des Lichtbogens zu gewährleisten. Bei einem langsam ansteigenden Ueberstrom wird die Masse 16 bewegt und ^G wird niemals die Zerreisspannung des Schaltelementes überschreiten. Die Werte von m und K sind zweckmässig unter Verwendung einer Zweiweg-Gedächtnislegierung für das Schaltelement so gewählt, dass das Schaltelement durch Kühlung zurückverformt wird, vergleiche Fig. 2b, nachdem ein Ueberstrom mit unterkritischem Anstieg vorbei ist. Dieser Thermoschalter kann auch mit einem Schaltelement mit einem Einweggedächtniseffekt verwendet werden, wobei Formänderungen bis zu etwa 8 % nutzbar sind. Anstelle einer direkten Unterbrechung des Stromkreises kann die Lageveränderung beim Zerreissen des Schaltelementes in bekannter Weise als Mittel zum Auslösen eines anderen Schaltvorganges, erforderlichenfalls mit zwischengeschaltsten Verstärkung des Schaltsignals, verwendet werden. Der als elektrische Sicherung wirkende Thermoschaltar gemäss Fig. 3 ist anstelle einer Schmelzsicherung in einem konventionellen thermoelektrischen Schalter 50 gemäss Fig. 8 verwendbar, der zur Sicherung elektrischer Stromkreise gegen langsam oder stossartig zunehmende Ueberströme bekannt ist.The thermal switch shown schematically in FIG. 3 consists of the switching element 18 in the form of a round rod or wire 6.5 mm in length and 0.33 mm ^{2 in} cross section made of an alloy of 3 M% Ni, 13 M% Al and 84 M% Cu, compare wire number 9 in Tables 1 and 2. Another example of a switching element is designated there with wire number 8. The upper end of the switching element 18 is held in an upper holder 19 which is immovably attached to a fastening 40. The lower end of the switching element is coupled via a holder 15 with an adjustable mass 16 of 14.8 g and a tension spring 14, which can also be omitted and is set with the spring constant K = 0 in the present example. The tension spring is held immovably on one side in a fastening 13. Mass 16 and tension spring 14 act together as a tensioning device and generate a mechanical tension that in the low temperature phase due to expansion of pseudo-plastic deformed switching elements 18, which is below its tensile stress. A current I is sent through the switching element at a room temperature of 20 ^° C., which is to be monitored for the occurrence of an overcurrent. Exceeds the current-time integral

within a time interval with 4t = 2 ms the value of SZ = ₁₀₀₀ A ² s, the switching element 18 tears and interrupts the circuit, as shown in Fig. 3b. The switching element acts as an electrical fuse with adjustable sensitivity. If the current rise is faster than a predeterminable value, the mechanical stress σ exceeds the tensile stress of the switching element before the mass 16 begins to move. The initial shape of the switching element is chosen so that the distance between the fragments after tearing is large enough to ensure separation of the arc. With a slowly rising overcurrent, the mass 16 is moved and ^G will never exceed the breaking voltage of the switching element. The values of m and K are expediently selected using a two-way memory alloy for the switching element in such a way that the switching element is deformed back by cooling, compare FIG. 2b after an overcurrent with a subcritical increase has passed. This thermal switch can also be used with a switching element with a one-way memory effect, whereby changes in shape can be used up to about 8%. Instead of a direct interruption of the circuit, the change in position when tearing of the switching element can be used in a known manner as a means for triggering another switching operation, if necessary with interposed amplification of the switching signal. 3 can be used in place of a fuse in a conventional thermoelectric switch 50 according to FIG. 8, which is known for securing electrical circuits against slowly or suddenly increasing overcurrents.

8a shows such a thermoelectric switch 50 in a semi-schematic representation, but with a thermal switch 38 which has a switching element 18 with a two-way memory effect, which does not tear when heated and thus cannot directly interrupt the circuit. In contrast to the thermal switch according to FIG. 3, the upper holder 19 of the switching element 18 is not immovably mounted in the thermal switch 38, but is connected to a linkage 12 in the catch arm 23 via a mechanical coupling 20 and is movable against a tension spring 11.

The electrical circuit goes from a connecting line 7 via a fixed contact 6, a contact end 8 of a contact arm 4, which can be pivoted about a linkage 1, via a connecting line 28, an additional securing element 9, a connecting line 22, the upper holder 19 through the switching element 18 lower bracket 15 to a connecting line 17th

• 1) die Anlenkung 12 gegen die Federkraft der Zugfeder 11 nach unten versetzt und
• 2) die Masse 16 und die mit ihr gekoppelte Zugfeder 14 aufwärts bewegt.

If an overcurrent flows through the switching element, which leads to a change in shape or here to contraction due to the shape memory effect, then

• 1) the linkage 12 against the spring force of the tension spring 11 down and
• 2) the mass 16 and the tension spring 14 coupled to it move upwards.

The movement time Δt _m according to equation (8) is characteristic of the second movement. As soon as the movement is completed, the tension σ disappears, see equation (11).

The first movement will only trigger the switch 50 if σ rises above a predeterminable critical value, which for translation of the articulation 12 downwards by e.g. 1 mm is sufficient. Otherwise, the switching element 18 is reshaped due to the setting of the values of mass 16 and spring force K of the tension spring 14 after passing through a critical overcurrent by cooling.

However, if the articulation 12 is deflected downward, the catch arm 23 is pivoted clockwise by an articulation 21, as indicated by dashed lines, and releases an angle arm 37 for pivoting counterclockwise. This pivoting is blocked as long as a hook end 25 of the catch arm 23 bears against a catch end 24 of the angle arm 37. Under the action of a compression spring 2, which is supported on a fastening 3 'and which tries to move the contact arm 4 by its articulation 1 clockwise, the angle arm 37 is pivoted counterclockwise by means of a thrust arm 29 by an articulation 26, as in FIG 8b. The contact arm 4 stands out from the fixed contact 6 and interrupts the electrical connection between the Connection line 7 and the connecting line 28. The push arm 29 is connected to the contact arm 4 by a linkage 5. At its lower end it has a linkage 27 which can slide in an opening 36 in the angle arm 37 when the angle arm is pivoted. When pivoting, the linkage 27 slides to the left in the opening 36, as a result of which the reset lever 32, which can also be pivoted about the linkage 27, is moved into an off position shown in FIG. 8c by means of a push arm 30. The reset lever 32 is under the tension of a tension spring 34, which is anchored in a fastening 37. It is connected to one end of the thrust arm 30 via a movable linkage 31. The other end of the push arm 30 is connected to the push arm 29 by the movable link 27. The switch 50 can also be switched on again with the reset lever 32 by pivoting it clockwise.

The thermal switches according to FIGS. 3 and 8a, reference number 38, are expediently used in addition to an additional switching element 9 which can be connected to the catch arm 23 by means of a mechanical coupling 10 and which responds to other parameters relevant to protection technology.

Rated values for switching elements 18 which are suitable for use in the thermal switch 38 are given in Tables 1 and 2 under wire numbers 1 to 7. The values in Table 1 apply to a room temperature of 20 ^o C, a deflection by one of the shape memory effects of 1 mm and a spring constant K = 0 of the tension spring 14. The tension spring 14 can be omitted from the two thermal switches described, but it is suitable for stabilizing the position the thermal switch and for application a bias on the switching element 18.

For the shape memory alloy of the switching element 18, alloys based on Ni Ti, Ni Ti Cu according to DE-OS 2 644 041, Cu Zn, Cu Al, Ni Zn are also particularly suitable, inter alia with ternary and other components, in terms of the material properties and the price such as Cu Al Ni, Cu Zn Al Ni etc.

It goes without saying that the invention is not limited to the above. For example, the shape of the switching element 18 can be strip-shaped, tubular, spiral-shaped, curved, etc. The switching element can be deformed by bending, twisting, compressing or stretching. A thermoelectric switch 50 according to FIG. 8 can be triggered by pulling or pushing. The change in position caused by the switching element can be detected in a known manner, for example by means of optical, electrical or hydraulic detectors, amplified and transferred to another switching element.

B e z e i c h n u n g s l i s t e

• 1 articulation of 4
• 2 compression springs
• 3 attachment of 2
• 4 contact arm
• 5 articulation
• 6 fixed contact
• 7 connecting cable
• 8 contact end of 4
• 9 fuse element
• 10 mechanical coupling
• 11 tension spring
• 12 linkage
• 13 attachment of 14
• 14 tension spring
• 15 lower bracket of 18
• 16 mass
• 17 connecting cable
• 18 triggering switching element
• 19 upper bracket of 18
• 20 mechanical coupling
• 21 articulation of 23
• 22 connecting line
• 23 tentacle
• 24 catches out of 37
• 25 hook end of 23
• 26 articulation of 37
• 27 linkage
• 28 connecting line
• 29 thrust arm
• 30 thrust arm
• 31 linkage
• 32 reset lever
• 33 linkage
• 34 tension spring
• 35 attachment of 34
• 36 breakthrough of 37
• 37 angle arm
• 38 thermal switch
• 40 attachment
• 41 converters
• 42 converters
• 43 comparators
• 50 switches
• A austenite
• C specific heat capacity
• d relative density
• f (t) time-dependent physical quantity
• F force
• g gravitational acceleration
• G chemical energy
• h specific enthalpy
• I electrical current
• K spring constant
• 1 length
• m mass
• M martensite
• q cross-sectional area
• Q (t) time-dependent energy
• s specific entropy
• t time
• t _m mechanical movement time
• T temperature
• U elastic energy of the spring
• x path, deflection
• x speed
• ẍ acceleration
• ẍ _G acceleration limit
• x _max maximum stretch
• y Switch output, switching signal
• y ₁ switching signal "On"
• ^y ₂ signal "Off"
• SZ current-time integral
• α damping constant
• elastic deformation
• ε _d applied by deformation
• relative shape change
• ε _M maximum relative shape change due to phase transformation
• Damping constant
• specific electrical resistance
• mechanical tension
• σ ₀ material constant
• 
  Phase angle
• ω angular frequency

Claims (11)

1. Thermal switch a) with a switching element that triggers the switching process (18) from a shape memory alloy b) with at least one switching device (14, 16; 11, 14, 16) interacting with this scarf element,
characterized in that c) this switching element thermally with a time-dependent physical variable f (t) and d) mechanically coupled to an adjustable mass (16) and that e) the thermal switch as a function of the exceeding of a predefinable limit value (x _G ) of the acceleration (x) caused by a change in temperature and shape in the switching element (18) assumes a switching position (y = y ₁ ; FIG. 8b) which characterizes this exceeding. 2. Thermal switch according to claim 1, characterized in that a) the switching element (18) arranged in a circuit of an electrical current to be switched. 3. Thermal switch according to claim 1 or 2, characterized in that a) the switching element (18) is coupled to a triggering device (23) of a switch (50). 4. Thermal switch according to claim 2 or 3, characterized in that a) the switching element (18) is immovably mounted on one side and b) the thermal switch, depending on the exceeding of the breaking voltage of the switching element, assumes a switching position which characterizes this exceeding (y = y ₁ ; Fi ^g. 8b). 5. Procedure for triggering a switching process a) depending on the exceeding of a time-dependent physical quantity (f (t)), b) which is transformed into a path-dependent and time-dependent variable (x) using a thermal switch, characterized in that c) this physical variable is transformed into a heat and time-dependent variable of a switching element (18), d) that this heat and time dependent variable is transformed into a path and time dependent variable (x (t)) and e) subjected to an acceleration detection (unterzogen) that f) the acceleration value (ẍ) is compared with a predefinable acceleration limit value (x _G ) and g) a switching signal (y = y _l ) is generated as a function of the exceeding of the limit value. 6. The method according to claim 5, characterized in that a) the acceleration limit value (x _G ) is set by means of a mass (16), b) the mass with the switching element (18) rigidly coupled and c) a switching element (18) made of a shape memory alloy is used that d) the switching element cooperates with a tensioning device (14, 16; 11, 14, 16), e) whose voltage applied to the switching element is sufficient to produce a pseudo-plastic deformation and thus to produce a shape memory effect in this switching element. 7. The method according to claim 6, characterized in that a) a shape memory alloy with a two-way memory effect is used for the switching element (18). 8. The method according to claim 7, characterized in that a) the switching element (18) is coupled to a triggering device (23) of a switch (50) and in addition to at least one additional fuse element (9) which is based on parameters relevant to protection technology other than the switching element (18) appeals, is used. 9. Method according to at least one of claims 5 to 8, characterized in that a) the initial temperature (T _AS ) of the phase transition of the shape memory alloy of the switching element (18) from the low to the high temperature phase is set by choosing the alloy composition and / or the mechanical preload of the switching element and that b) this initial temperature is assigned to an initial value of the physical quantity (f (t)) to be monitored for exceeding a limit value in such a way that a switching signal (y = y _l ) is only triggered when a predeterminable increase in this physical quantity is exceeded. _10th Method according to at least one of claims 5 to 9, characterized in that a) the switching element (18) is flowed through by an electrical current to be switched and b) generates a switching signal when the initial rise in an overcurrent exceeds a predeterminable value. 11. The method according to at least one of claims 5 to 10, characterized in that a) the switching element (18) is immovably mounted on one side, _b ) acts as a fuse and exceeding the tensile stress of the switching element as a criterion is used to trigger the switching signal (y = y ₁ ).

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