The present invention relates to an electrical fuse system. In particular, the electrical fuse system may be used within an aerosol generating device.

Fuses and circuit breakers are electrical safety devices that are operable to protect an electrical circuit in the event of excess current flowing through a conductor. In the absence of a fuse or circuit breaker, excess current may result in excessive heat generation, and a risk of damage and fire to equipment.

Typically, a fuse comprises a metal wire or strip that is configured to melt above a threshold current, such that the supply of current through the electrical circuit is interrupted. Hence, a fuse is considered to be a sacrificial device that must be replaced once it has served its function. In contrast, a circuit breaker is an automatically operated switch which, once it has operated to interrupt current flow within a circuit, may be reset (automatically or manually) to resume normal function.

Within battery operated electrical devices, such as aerosol generating devices, there is a need to provide an electrical safety device that is able to reliably prevent continued operation of the battery operated device when the battery has a fault condition. An object of the present invention is to address this need.

According to a first aspect of the invention, there is provided an electrical fuse system comprising: a chamber for receiving a battery; and an electrical contact disposed within the chamber and configured to conduct electricity between the battery and an electrical load, wherein the electrical contact comprises a shape memory alloy configured to move between a first position and a second position, wherein the shape memory alloy is arranged to form an interface with an electrical terminal of the battery in a first position, thereby forming an electrical path between the battery and the electrical load, wherein the shape memory alloy is arranged to disconnect from the electrical terminal of the battery in the second position, thereby disconnecting the electrical path between the battery and the electrical load, and wherein the shape memory alloy is configured to move from the first position to the second position when a temperature of the battery exceeds a threshold temperature.

In this way, when the battery overheats, which is indicative of a fault condition, the supply of current from the battery to an electrical load is interrupted. As a result, continued use of an electrical device in which the battery is disposed may be prevented when there is a fault in the battery, thereby improving the safety of the device. Advantageously, the shape memory alloy electrical contact is able to automatically disconnect the electrical path between the battery and electrical load when the battery exceeds the threshold temperature, without requiring user intervention or additional electronic diagnostics equipment and/or circuitry.

In one example, the battery may be considered to have a fault above 60°C. Therefore, the electrical contact may be configured to disconnect from the battery above a threshold temperature of 60°C. However, the skilled person will appreciate that the threshold temperature may vary according to the type of battery and the cell chemistry.

Preferably, the shape memory alloy is arranged to lie parallel to the electrical terminal of the battery at the interface in the first position. Preferably, the interface formed between the shape memory alloy and the electrical terminal of the battery in the first position is substantially planar. In this way, a large area of contact is provided between the electrical contact and the electrical terminal of the battery during normal operation, i.e. under the threshold temperature of the battery. Thus, a solid electrical interface is formed between the battery and electrical load which ensures that the electrical load remains reliably connected to the battery under the threshold temperature.

Preferably, the shape memory alloy is configured to retract in a direction perpendicular to the interface between the shape memory alloy and the electrical terminal of the battery when moving from the first position to the second position. In this way, the direction of movement of the shape memory alloy is configured such that the shape memory alloy is unlikely to accidentally disconnect from the electrical terminal of the battery. In contrast, within known fuse systems, electrical contacts are often configured in a manner that renders them susceptible to deforming under small forces, such as when the electrical fuse system is dropped. For example, previous devices have been known to utilise an electrical contact having a cantilever arrangement (e.g. a bimetallic strip) that is highly susceptible to deformation. As a result, in such devices, the electrical circuit may often be inadvertently disconnected below the threshold temperature.

Preferably, the shape memory alloy has a planar surface, and the planar surface is arranged to form the interface with the electrical terminal of the battery.

Preferably, the shape memory alloy has a curved surface, and a maximum of the curved surface is arranged to form the interface with the electrical terminal of the battery. In this way, an electrical interface is formed between the battery and the electrical contact which is resistant to shock and impact forces, and which is reliably able to conduct electricity between the battery and the electrical load below the threshold temperature.

Preferably, the shape memory alloy is substantially “U”-shaped, and an apex of the “U” is arranged to form the interface with the electrical terminal of the battery. Preferably, the shape memory alloy is substantially dome-shaped, and an apex of the dome is arranged to form the interface with the electrical terminal of the battery.

Preferably, the shape memory alloy is configured to increase a radius of curvature of the curved surface when moving from the first position to the second position, such that the shape memory alloy retracts from the electrical terminal of the battery. In this way, the electrical fuse system provides a secure contact between the battery and the electrical contact under normal operating conditions, i.e. under the threshold temperature, whilst also providing a reliable mechanism that is able to disconnect the battery from the electrical contact when the battery overheats, i.e. above the threshold temperature.

Preferably, the shape memory alloy is a one-way shape memory alloy. Once a battery has overheated, it may be unsafe to operate even after the battery has cooling back down to a normal operating temperature. Hence, by using a one way shape memory alloy as the electrical contact, it is possible to ensure that the battery cannot supply electrical power to the electrical load, even after the battery has cooled back below the threshold temperature. This leads to improved safety of the electrical fuse system.

Preferably, the electrical contact comprises a spring-loaded electrical contact. Preferably, the spring-loaded electrical contact is configured to be compressed when the battery is received within the chamber such that a restoring force is applied to the battery, thereby holding the battery within the chamber. In this way, the battery may be positioned and held within the chamber without requiring soldering between the battery and the chamber and/or electrical contact. Advantageously, this allows for the replacement of spent or damaged batteries at a low cost and with minimal labour.

According to another aspect of the invention, there is provided an aerosol generating device comprising an electrical fuse system according to the above aspect.

Embodiments of the invention are now described, by way of example, with reference to the drawings, in which:

Figures 1A and 1 B show an electrical fuse system having an electrical contact in a first position and a second position respectively according to a first embodiment of the invention;

Figures 2A and 2B show an electrical fuse system having an electrical contact in a first position and a second position respectively according to a second embodiment of the invention; and

Figures 3A and 3B show exemplary configurations of the electrical fuse system according to the first embodiment of the invention.

Figures 1A and 1 B illustrate an electrical fuse system 2 (i.e. a circuit breaker, or switch) according to a first embodiment of the invention. The electrical fuse system 2 comprises an electrical contact 4 disposed within a chamber 6, wherein the chamber 6 is configured for receiving a battery 8. The electrical contact 4 is configured to move from a first position (as seen in Figure 1A) to a second position (as seen in Figure 1B).

The chamber 6 is defined by and/or disposed within a housing 12. For example, the housing 12 (and chamber 6) may be a constituent of an electrical device, such as an aerosol generating device.

The electrical contact 4 is attached to a wall of the chamber 6. A conduction path 16 extends from the electrical contact 4 to an electrical load 14. The electrical contact 4 is configured for conducting electricity from the battery 8 received within the chamber 6 to the electrical load 14 via the conduction path 16. For example, if the electrical contact 4 is disposed within an aerosol generating device, the electrical load 14 may correspond to a heating element. Of course, the skilled person will appreciate that the electrical load 14 is not limited to a heating element, and may comprise a range of electrical components.

The electrical contact 4 comprises a first planar surface 7 arranged to face into the chamber 6. For example, the electrical contact 4 may be formed as a cylinder, conical frustum, pyramidal frustum, cuboid, or other shape with at least one planar surface, and preferably two parallel planar surfaces.

In use, the battery 8 may be positioned within the chamber 6 such that, in the first position, the electrical contact 4 forms an interface 5 with an electrical terminal 10 of the battery 8. In particular, the first planar surface 7 of the electrical contact 4 is arranged to abut against (i.e. contact) a second planar surface 9 of the electrical terminal 10 of the battery 8. In this way, an electrical path is formed between the battery 8 and the electrical load 14, and the battery 8 is able to power the electrical load 14.

The interface 5 formed between the electrical contact 4 and the electrical terminal 10 of the battery 8 is substantially planar. The first planar surface 7 of the electrical contact 4 and the second planar surface 9 of the electrical terminal 10 are flat and lie parallel to one another. Preferably, the electrical terminal 10 may also be formed as a shape having at least one planar surface, and more preferably two parallel planar surfaces. However, the skilled person will appreciate that the electrical terminal 10 may also be formed without a planar surface. For example, the electrical terminal 10 may comprise a non-planar (e.g. rounded) surface, and the first planar surface 7 of the electrical contact 4 may contact the non-planar surface.

Advantageously, the planar interface 5 provides a large contact area between the electrical contact 4 and the electrical terminal 10 of the battery 8, thereby providing a reliable conduction path that is less likely to separate under an impact (e.g. dropping the electrical fuse system 2) or other applied force.

The electrical contact 4 comprises (and optionally consists of) a shape memory alloy. The shape memory alloy exhibits the shape memory effect such that it deforms (i.e. undergoes a phase transformation) as a function of temperature. In particular, the shape memory alloy is configured to deform when the temperature of the battery 8 exceeds a threshold temperature, such that the electrical contact 4 moves from the first position to the second position. In one example, the battery 8 may heat the electrical contact 4 such that the battery 8 and the electrical contact 4 share the same temperature. In this case, the threshold temperature may correspond to the martensitic transformation temperature of the shape memory alloy. Alternatively, the battery 8 may heat the electrical contact 4 such that the electrical contact 4 has a lower temperature than the battery 8. In this case, the threshold temperature 8 may be higher than the martensitic transformation of the shape memory alloy, and the shape memory alloy may be configured to reach the transformation temperature when the battery 8 reaches the threshold temperature.

In one example, the battery 8 may be considered to have a fault above 60°C. Thus, the threshold temperature of the battery 8 may be 60°C. However, the skilled person will appreciate that the threshold temperature will vary according to the type of battery and the cell chemistry. The shape memory alloy may comprise Ni-Ti, Cu-AI-Ni, Cu-Zn-AI or other suitable shape memory alloys. Preferably, the shape memory alloy comprises a one-way shape memory alloy. In this way, the battery 8 is prevented from supplying power to the electrical load 14 after the battery 8 has cooled back below the threshold temperature. In other examples, the shape memory alloy may comprise a two-way shape memory alloy, such that the electrical path between the battery 8 and the electrical load 14 may be reconnected once the battery 8 cools back below the threshold temperature.

In use, when the battery 8 exceeds the threshold temperature (e.g. when the battery has a fault condition), the shape memory alloy is configured to deform such that the electrical contact 4 retracts from the electrical terminal 10 of the battery 8, and moves from the first position to the second position. Hence, the electrical contact 4 is disconnected from the battery 8 and the electrical path between the battery 8 and the electrical load 14 is broken (i.e. disconnected).

The electrical contact 4 is configured to retract from the electrical terminal 10 of the battery 8 in a direction perpendicular to the interface 5. In other words, the shape memory alloy is configured to undergo a shape change such that the first planar surface 7 of the electrical contact 4 is moved away from the second planar surface 9 of the electrical terminal 10, in a direction perpendicular to the first planar surface 7.

Figures 2A and 2B illustrate an electrical fuse system 20 according to a second embodiment of the invention.

The electrical fuse system 20 comprises an electronic contact 22 with similar properties to the electrical contact 4 described in the previous embodiment. However, in this embodiment, the electrical contact 22 is formed in a curved shape, i.e. as an arc of shape memory alloy, with an apex 24 (or maximum) that faces into the chamber 6.

In one example, the electrical contact 22 may be formed as a “U”-shape. In another example, the electrical contact 22 may be formed as a dome shape. Again, the electrical contact 22 is configured to move from a first position (as seen in Figure 2A) to a second position (as seen in Figure 2B), when the temperature of the battery 8 exceeds the threshold temperature.

The electrical contact 22 is configured such that, in the first position, the apex 24 of the electrical contact 22 contacts and forms an interface 26 with the electrical terminal 10 of battery 8 received within the chamber 6. In this example, the apex 24 abuts the second planar surface 9 of the electrical terminal 10. However, in other examples, the electrical terminal 10 may comprise a non-planar (e.g. rounded) surface, and the apex 24 may contact the non-planar surface.

The shape memory alloy is configured to deform when the battery 8 exceeds the threshold temperature such that the electrical contact 24 retracts from the electrical terminal 10 of the battery 8. In particular, the shape memory alloy is configured to undergo a shape transformation in which the radius of curvature of the electrical contact 22 increases and the apex 24 moves away from the electrical terminal 10 of the battery 8, in a direction perpendicular to a tangent to the apex 24. In others words, when moving from the first position to the second position, the electrical contact 22 flattens towards the wall of the chamber 6. Hence, the electrical contact 22 disconnects from the battery 8 in the second position, and the electrical path between the battery 8 and the electrical load 14 is broken (i.e. disconnected).

The electrical contact 22 may be a spring-loaded electrical contact that is operable to deform under an applied force and provide a restoring force. For example, in the first position illustrated in Figure 2A, the electrical contact 22 may be subject to a compressive force due to the presence and constraint imposed by the battery 8, such that that electrical contact 22 is compressed towards the wall of the chamber 6. As a result of the compression, the electrical contact 22 may generate a restoring force which is applied against the electrical terminal 10 of the battery 8. The restoring force is operable to hold the battery 8 in a stable position within the chamber 6. In this way, the battery 8 may be removed and replaced within the chamber 6 without requiring solder, adhesive or other fixing means to secure the battery 8 within the chamber 6. The skilled person will appreciate that the electrical contact 4 of the first embodiment may also be configured as a spring-loaded electrical contact.

Figures 3A and 3B illustrate a specific embodiment of the electrical fuse system 2 according to the present invention, with exemplary dimensions provided. Figures 3A and 3B have corresponding features to those shown in Figures 1A and 1 B (although they are not labelled in Figures 3A and 3B for clarity purposes).

In the exemplary embodiment shown in Figures 3A and 3B, all of the dimensions are provided in mm. As previously discussed, the chamber 6 is configured for receiving the battery 8. The battery 8 has a height of 65 mm and a width (e.g. diameter) of 18 mm. In the first position, the electrical contact 4 has a height (e.g. distance between the first planar surface 7 and the surface attached to the wall of the chamber 6) of 10 mm. In the second position, the electrical contact 4 undergoes a shape change such that it reduces in height by 50%, i.e. it has a height of 5 mm. The width of the electrical contact is 10 mm.

Again, it will be understood that this specific embodiment is simply an exemplary embodiment according to the invention, and the invention is not intended to be limited in any way, shape or form by the dimensions provided for this exemplary embodiment.

Moreover, it will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention. It should also be appreciated that particular combinations of the various features described and defined in any aspects described herein can be implemented and/or supplied and/or used independently.