Patent Application
20090218530
This invention relates to a heater insert with an electric resistance heating element and at least one electric connector lead through which the heating element can be supplied with power. The invention furthermore relates to an expansion material element with a housing and a movable actuation pin passed out of the housing, with the expansion material and such a heater insert being provided in the housing.
Such a heater insert and a heatable expansion material working element are known from WO 02/086646, for example.
Expansion material working elements are used in particular for actuating thermostat valves. In the housing of the expansion material working element, the heater insert heats up the expansion material so that the expansion material expands and pushes the actuation pin out of the housing. A thermostat valve can thus be controlled by supplying electric power to the heater insert.
When heating the expansion material, paraffin for example, a pressure of up to 300 bar arises in the housing of the expansion material working element. Requirements on the tight seal of the expansion material working element are high due to this pressure, in combination with the expansion material's reduced viscosity at elevated temperatures.
One weak point through which expansion material can escape is, in particular, the heater insert with its opening for the at least one connector lead (as a rule, two connector leads are provided).
In the heater insert known from U.S. Pat. No. 7,172,133, the connector leads are embedded in a solid plastic base which is sealed off by an O-ring towards the housing of the expansion material working element.
It has been shown that, during operation, small amounts of expansion material escape through the seal formed by such a plastic base. In the course of time, this results in a reduction of the working stroke and the reaction times of the expansion material working element since a smaller amount of expansion material must be heated up to correspondingly higher temperatures until sufficient pressure is built up to push the actuation pin by the desired length from the housing.
Furthermore, utmost care must be taken in the assembly of the expansion material working element so that no leakage points result through which expansion material can escape between the heater insert and the housing since the plastic base may not be subjected to any major mechanical load.
Accordingly, it is an object of the invention to show a way of how an improved seal can be economically provided for a heater insert of the above-mentioned type and of how such a heater insert can be more easily mounted with a housing.
This object is solved according to the invention by a heater insert with an electric resistance heating element, at least one electric connector lead through which the heating element can be supplied with power, a metal body with a connecting opening through which the at least one connector lead is passed, and a duct seal by means of which the connecting opening is closed, the duct seal being formed with a glass body as a compressed glass-to-metal seal.
A compressed glass-to-metal seal takes advantage of the fact that the metal body has a considerably higher coefficient of thermal expansion than the glass body it surrounds. To produce a compressed glass-to-metal seal, the metal body is heated and glass introduced into the connecting opening with the connector lead passing through it. Upon cooling down to room temperature, the glass body solidifies and contracts. Due to its higher coefficient of thermal expansion, the metal body contracts more than the glass body so that the glass body is pressed with considerable pressure against the embedded connector lead. Thus, a compressed glass-to-metal seal provides an excellent seal not only between the glass body and the penetrating connector lead(s), but also between the glass body and the surrounding metal body.
Aside from the improved tightness, a heater insert according to the invention moreover has the essential advantage that the metal body surrounding the glass body can be combined much more easily with a housing—for example, the metal housing of an expansion material element—than the plastic bases common in prior art with embedded connector leads. This is due to the fact that the metal body can be exposed to considerably greater mechanical loads in the assembly process, due to its much greater hardness compared with plastic materials—without any resulting damages. Moreover, a metal body, a lathe-cut part for example, can be manufactured with smaller tolerances than a plastic part and for that reason can be more easily inserted into the housing of an expansion material working element with the precision required for a tight connection.
While heater inserts with their plastic bases, commonly used in prior art, had to be inserted into an upper, larger opening of a cylindrical housing and be pushed through the housing until the connector lead exits from a smaller opening at the bottom end of the cylindrical housing, a heater insert according to the invention can be inserted, for example, into a lower housing opening, and the edge of this housing opening can be rolled in or flanged to close the opening tightly. In addition, the metal body can be connected with a substance-to-substance bond or a material connection to the housing—it can be welded, in particular—so that an excellent seal can also be reliably provided between housing and metal body. No an additional seal like an O-ring is necessary. It is favorable in this respect to manufacture the housing and the metal body of steel, preferably of stainless steel.
Despite the relatively high expenditure of manufacturing a compressed glass-to-metal seal, a heater insert according to the invention can be produced at a rather reasonable price in comparison with heater inserts known from prior art with plastic bases in which the connector leads are embedded. This is due to the fact that a relatively expensive plastic injection mold is required for embedding the connector leads into plastic bases since the individual connector leads are difficult to handle here. For a heater insert according to the invention, the metal body can be manufactured inexpensively as a stamped part or, preferably, as a lathe-cut part into whose connecting opening a drop of glass can be introduced by relatively simple means to enclose the at least one connector lead.
An additional cost reduction can be achieved with a heater insert according to the invention which uses a nickel/iron alloy for the connector leads. This has the advantage that the at least one connector lead can be inexpensively connected to the heating element by means of welding. Furthermore, nickel/iron alloys have a coefficient of thermal expansion which is excellently suitable for a compressed glass-to-metal seal.
With little expenditure, a plastic body can be injection-molded onto the metal body of a heater insert according to the invention—for example, as a carrier for the heating element or on the other side of the compressed glass-to-metal seal, for example, as the body of a plug-in connector.
Instead of a plastic body, a ceramic body can also be used—especially of polymer ceramics.
Compressed glass-to-metal seals are known in other areas of technology, for example for the housings of electronic semiconductor components with integrated circuitry. For producing compressed glass-to-metal seals and for the selection of materials for the glass body and the metal body enclosing it, reference is made to EP 0574797 B1 which is incorporated by reference into the present application.
A heater insert according to the invention is particularly suitable for a heatable expansion material working element with a housing and a movable actuation pin passed out of the housing, with the expansion material and a heater insert according to the invention being provided in the housing. However, a heater insert according to the invention is also suitable per se for other devices. Accordingly, the subject matter of the invention is also the use of a compressed glass-to-metal seal a connector lead of a heater insert.
Depending on the application of a heater insert according to the invention, the metal body with the compressed glass-to-metal seal can be part of a base or/and part of a housing. In cases in which the heater insert is provided with its own housing, good thermal coupling of the heater insert to the housing is generally desired.
The invention relates furthermore to a thermostat valve with a heatable expansion material element in which a heater insert according to the invention is provided.
Additional advantages and features of the invention are explained on the basis of exemplary embodiments with reference to the enclosed drawings. In the Figures:
The expansion material working element 1 shown in
The expansion material 1d can be heated with the heater insert 1a so that pressure builds up in the housing 14 by means of which the actuation pin 1b, for example for controlling a thermostat valve, can be pushed out of the housing 14 in relation to the heat applied. Further details on the mode of functioning of heatable expansion material elements are disclosed in U.S. Pat. No. 7,172,133 and therefore need not be explained in more detail.
The heater insert 1a comprises an electric resistance heating element 3 in the form of a PTC heating wire of a nickel/iron alloy, a plastic carrier 2 around which the heating wire 3 is wound, and connector leads 5, 6 which are passed through a base 4. The connector leads 5, 6 are embedded over a part of their length in the plastic carrier 2. It is especially favorable when the resistance heating element 3 as well as the connector leads 5, 6 consist of nickel/iron alloys so that particularly good weldability is provided.
Instead of a heating wire, a thick-layer element can also be used, for example, as a resistance heating element which is held by a carrier, for example, of plastic or ceramic.
In the presented exemplary embodiment, the base is formed by a metal body 4 which is a lathe-cut part of stainless steel. It has a groove 13 in which an O-ring 15 is provided by means of which the metal body 4 is sealed off towards the housing 14. Alternatively, the metal body 4 can also be connected by a positive material connection with the housing 14, preferably by welding or brazing.
In a cross-sectional view,
To produce the compressed glass-to-metal seal, the metal body 4 was heated and the glass body 11 was introduced in liquid form in the passage channel. Upon cooling down to room temperature, the glass body 11 solidifies, with the metal body 4—due to its higher coefficient of thermal expansion—contracting more than the glass body 11. Thus, the metal body 4 is pressing with high pressure against the glass body 11 and it, in turn, against the connector leads 5, 6 so that an excellent seal results.
As seen in
On the side of the glass body 11 facing away from the plastic carrier 2, a plastic body 8 is injection-molded onto the metal body 4 in which the connector leads 5, 6 are embedded. Thus short circuiting by any unintentional contact between the connector leads 5, 6 or the metal body 4 is prevented. The connector leads 5, 6 feature a bend in their section which is embedded in the plastic body 8 so that the connector leads 5, 6 leave the plastic body 8 with greater spacing between each other.
Thus, despite the small inside diameter of the connecting opening 7 and a diameter of the connector leads 5, 6 of preferably 0.8 mm to 1.2 mm, a space between the two connector leads 5, 6 is achieved by means of which short-circuiting due to any unintentional contact between the connector leads 5, 6 or the metal body 4 can be excluded.
For many applications, the outside diameter of the metal body 4 may not exceed a value of 12 mm, preferably 10 mm in the area of the glass body 11. So that the metal body 4 is not deformed—under the pressure developing during cooling due to the different coefficients of thermal expansion—which might result in an undesirable decrease of the pressure and thus to possible leaks, thickness of its walls in the area of the glass body 11 should amount to at least 0.8 mm, preferably to 1.0 mm, better to at least 1.5 mm. Due to the increasing miniaturization of thermostat valves, the inside diameter of the connecting opening of the passage channel is thus preferably approximately 4 mm to 6 mm. These data apply in case that only one connecting opening is provided. The inside diameters and wall gauges can be reduced in case of a metal body 4 with two connecting openings through which one connector lead each is passed through.
In the exemplary embodiment described, the metal body 4 of the heater insert 1a comprises a connecting opening 7 through which two connector leads 5, 6 are passed. It is also possible, however, to provide a separate connecting opening in the metal body 4 for each connector lead. Then, according to
The exemplary embodiment shown in
A particularly strong and heavy-duty connection of the plastic carrier 2 with the metal body 4 can be achieved, in particular, by the connecting opening 7 of the metal body 4 being undercut so that the plastic carrier has a positive fit connection with the metal body 4. An undercut 31 of the metal body 4 is advantageous not only with the preferred injection molding of the plastic carrier 2 to the metal body 4 but also for the adhesive bonding and/or clipping of the plastic carrier 2 into the metal body 4.
In the presented exemplary embodiment, the connecting openings 7 are formed as bore holes in the metal body 4 between the cylindrical blind holes 32 and are accordingly circular. The use of two connecting openings for the two connector leads 5, 6 has the advantage that, for sealing the connecting openings 7, smaller glass bodies 11 are sufficient and consequently, the wall thickness of the metal body 4 in the area of the glass bodies 11 can be reduced. The heater insert 1a can thus be produced smaller overall and more compact. Furthermore, straight guiding of the connector leads 5, 6 is facilitated by thinner outside walls of the metal body 4. The outside wall thickness for a metal body 4 with two connecting openings 7 through which one connector lead each is passed preferably lies between 0.5 mm and 1 mm, especially preferably between 0.6 mm and 0.8 mm. The diameter of the connecting openings preferably lies between 1.5 mm and 2.5 mm, especially preferably between 1.8 mm and 2.2 mm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 013 661.3 | Mar 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/002311 | 3/14/2006 | WO | 00 | 10/6/2008 |
