Power plants – Motor operated by expansion and/or contraction of a unit of... – Mass is a solid
Reexamination Certificate
1999-07-09
2001-06-05
Nguyen, Hoang (Department: 3748)
Power plants
Motor operated by expansion and/or contraction of a unit of...
Mass is a solid
C060S528000
Reexamination Certificate
active
06240728
ABSTRACT:
DESCRIPTION
The present invention refers to an electromechanical device, such as for instance an actuator device, as defined in the preamble of claim
1
, and to a method to insulate components of an electromechanical device from the environment, as defined in the preamble of claim
22
; the features of the preamble of said claims are known for instance from BE-A-542.149, which describes a manual safety switch.
Electromechanical devices are known, which comprise a housing within which electrical components and movable mechanical elements or kinematic motions are contained, often near to each other. Let us think for instance of electrothermal actuator devices applied in various fields, including domestic appliances and environment air conditioning. Said electrothermal devices usually comprise an external housing, for example in thermoplastic material, wherein a thermoactuator and at least partially a movable operating shaft are contained.
The thermoactuator comprises a body made of electrically and thermally conductive material (for instance steel), containing a thermally expansible material (such as for instance wax), wherein a sliding thruster element is embedded. Said body is in contact with an electric heater, typically consisting of a resistor with a positive temperature coefficient (PTC), which is electrically supplied by two terminals.
When electric voltage is supplied to the supply terminals, the heater generates heat and causes the expansion of the thermally expansible material. Such an expansion causes the thruster to make a linear displacement outside the thermoactuator body; the thrust generated by the thruster is therefore transferred to the above shaft that will move linearly till it reaches a stable work position generally determined by a mechanical limit stop, provided inside the housing of device. When the power supply stops, the heater cools down and the thermoexpansible material will shrink causing both the thruster and the shaft to go back to their initial rest positions, respectively, with the aid of an elastic return element, such as a spring.
The present invention basically acknowledges that, in some applications, the electric components of certain electromechanical devices may be subject to malfunction risks, due to the aggressive influence of external agents in the environment.
This may for instance happen when the above thermoelectric actuators are used in air conditioning or air cleaning systems, where the air to be conveyed or cleaned contains aggressive agents or contaminant substances, which may favour a development of electric discharges or electric energy leakages, overabsorptions or short-circuits with ensuing faults of the device itself.
Another critical application field is represented by household appliances, where said thermoelectric actuators may be located near water and/or detergent agent dispensers, whose likely losses might cause the above contamination with damaging effects for the device.
Therefore, under these circumstances, the use of electrically controlled actuator devices is rather problematic, above all when such devices need to be small sized, so that electrical parts are necessarily placed near movable mechanical components. Apparently, to obviate to this problem it would be enough to provide an airtight sealing for the housing of the device that contains the live electric components.
However, the housings of the actuator devices of the type commonly used are not fit as such to warrant such a sealing from the environment, due to the presence of openings needed for the outcoming of movable mechanical components or of fissures due to an imperfect coupling of the external shells of the housing (to this purpose it should be noted that such components are commonly subject to shrinkage and/or stresses during the molding cycle of thermoplastic material).
Manufacture of special airtight housings, for instance through insertion of perimetral gaskets, would increase the overall dimensions of the device and make the productive process of the device rather complex, with a consequent increase of manufacturing time and costs.
A possible option would be to inject a suitable material inside the housing of the electromechanical device, capable of insulating the internal live components from the environment; however, also this solution appears somewhat problematic.
A first difficulty, for instance, is due to the need of fully coating the electrical components of the device, but without any interference with the motion of the mechanical elements located nearby. A further difficulty consists in ensuring a fast filling (normally in the order of a few seconds) of the area to be insulated in order to allow for an automated manufacturing process. The filling material should also set very quickly to allow immediate handling of the device and avoid leakage from the joining areas of the relevant housing.
Finally, said filling material should be easily removable in case of accidental leaking from the housing during the injection operation.
It should also be considered, when insulating electrothermal devices, that the filling material must be suitable to withstand high temperatures over a long time, which in the instance of thermoactuators normally reach about 200° C.
In order to better highlight the problems at the base of this invention, reference will be made in the following to a thermal electromechanical device, i.e. a thermoactuator, which reflects a whole number of unfavorable characteristics for the use of classic filling and/or insulating materials, as mentioned hereafter.
It is known to make use of certain resins to insulate electronic circuits from the environment, which are usually poured at room temperature into a housing containing the circuit.
In different applications, other fluid resins are injected at high temperature in a body or mold, where they set fast while cooling down; other resins are mixed at room temperature with a catalyst element suitable to determine a fast setting of the resin; further types of resins are also injected at room temperature and hardened by external heat or ultraviolet rays.
Said resins may initially appear as a fluid or viscous material, which becomes a very hard glassy material following reticulation or transformation process.
As already mentioned, resins with a low working temperature cannot be employed for a thermoactuator, as they would be degraded by the high temperature of the heating elements. Also the resins becoming very rigid after their process are not suitable for such an application, since they do not allow any mechanical expansion. Let us think for instance of the electric heater used in a thermoactuator, which tends to expand during operation under temperature; if rigid resins were used, the heater would be mechanically stressed by its own expansion with the risk of failure (for this reason, PTCs, usually made of ceramic material, would be subject to failure). At any rate, resins generally have a highly compact volume tending to stick or block all components they come in contact with; even in case of very small metering errors of the injected material, there would be some jamming up risks for the movable actuation elements or kinematic motions inside the housing of the device. Such a jamming risk is stressed by the fact that said filling should be executed very fast by automatic systems, through which small, but exact, volumes of material can be injected.
The likely use of very fluid filling materials would ensure fast filling, but cause a risk of leakage from the housing joints; on the other hand, the use of less fluid materials would increase manufacturing cycle time, requiring longer dwelling times for a correct setting of the insulating material inside the housing.
To obtain insulation from the environment some silicone resins are also known, which if injected in the housing of an actuator device, would neither cause any stressing under normal temperature thanks to their flexibility nor would be subject to degradation with high temperatures.
However, also silicones would tend for their own
Eltek S.p.A.
Levine & Mandelbaum
Nguyen Hoang
LandOfFree
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