EP0806000A1

EP0806000A1 - Temperature sensing device

Info

Publication number: EP0806000A1
Application number: EP95940498A
Authority: EP
Inventors: Carl-Eric Berg
Original assignee: Arcu Formplast AB
Current assignee: Arcu Formplast AB
Priority date: 1994-12-02
Filing date: 1995-11-30
Publication date: 1997-11-12
Also published as: NO972146D0; SE9404199L; SE502895C2; FI971917A0; FI971917L; FI971917A7; SE9404199D0; NO972146L; WO1996017281A1

Abstract

A temperature sensing device adapted to bring about an actuating movement of a control valve, e.g. for a heating element. The device comprises a heat insulating housing (2) with a closed fluid chamber (5), which is filled with a fluid having a high coefficient of volume expansion and which is enclosed externally by a heat conducting casing (4) and internally by an elastically stretchable diaphragm (7). The diaphragm abuts a piston (9), which is displaceable in a sleeve body (6, 6') in the housing (2). The piston and the surrounding sleeve body (6, 6') form a continuous abutment surface for the diaphragm (7), wherein the central portion (7f) of the diaphragm (7) continuously abuts the end surface of the piston (9) and follows the movements of the piston while being stretched. The various parts of the device are preferably made of a polymer material.

Description

TEMPERATURE SENSING DEVICE

The invention concerns a temperature sensing device adapted to bring about an actuating movement of a control valve for a heating medium, comprising a housing with a closed fluid chamber, which is filled with a fluid having a high coefficient of volume expansion and which is enclosed externally by a heat conducting casing and internally by an elastically stretchable diaphragm abutting an axially movable actuating means in order to bring about said actuating movement during temperature variations in the ambient region of said casing.

Such temperature sensing devices are generally known and are used as thermostats, i.a. at heating elements, in particular at water based heat radiators for controlled room heating.

However, the known devices are fairly complicated and expensive to manufacture. As a rule, the external, heat conducting casing is made of metal as are most of the internal components in the device. The diaphragm can be formed as a bellows to enable a sufficient axial stroke and, furthermore, complicated safety devices are normally required to prevent the diaphragm from bursting at elevated temperatures. See e.g. US-A-4 508 262 (Danfoss AS) relating to a temperature sensing device with a rotatable casing permitting the setting of a desired tempera- ture reference value.

The main object of the present invention is to accomplish a substantially simpler temperature sensing device having only a few components, which are inexpensive to manufacture and assemble and which provides a high temperature sensitivity in spite of its simple structure and has a relatively large stroke of the actuating means without risking that the diaphragm bursts while being stretched. Moreover, the sensing device should not be influenced very much by the heat transfer from the heating medium. Rather it should operate substantially in response to the temperature of the ambient region of the casing. Further, secondary objects are to enable an inherent safety function at elevated temperatures and to enable a choice of materials being advantageous from an environmental point of view.

The above mentioned main object is achieved for a temperature sensing device formed in accordance with claim 1, whereas the secondary objects are achieved for devices as stated in claim 8 and claim 6, respectively.

With the structure stated in claim 1, it is possible to bring about an effective and quick transfer of heat to the whole volume of the fluid in spite of relatively small dimensions of the device as a whole, and to achieve a relatively long axial movement of the actuating means, in the form of a piston, while making use of the elastic stretchability of the diaphragm material in a positive way. The operational region of the piston is located adjacent to an end surface of a surrounding sleeve body, and the diaphragm is preferably stretched in opposite directions in the respective end positions. Thus, the device has a great temperature sensitivity and, moreover, the heat insulating housing provides a good shielding against heat radiation and heat conduction from the heating medium being present nearby.

The structure according to claim 2, with internal flanges, ridges or grooves at the inside of the casing, provides an especially good heat transfer and temperature sensitivity.

The device according to claim 6, with parts made of a polymer material, involves a low manufacturing cost in series produc¬ tion and a product being positive to the environment.

The embodiment according to claim 8, with a sleeve being biassed by a safety spring, provides a good safety function, wherein the stretching of the diaphragm may even be reduced when the sleeve is displaced at elevated temperatures. Further advantageous features will appear from the detailed description below involving two embodiments of the invention, reference being made to the appended drawings.

Figure 1 is a central longitudinal section through a first embodiment of the temperature sensing device according to the invention; and

Figures 2a, 2b and 2c are central longitudinal sections through a second embodiment of the temperature sensing device according to the invention, the device being illustrated in three different positions corresponding to three different tempera¬ tures.

The temperature sensing device shown in figure 1 is intended to be mounted on a control valve (not shown) for a heating medium, e.g. water in a heat radiator for control room heating. It is understood that the control valve of the heating element is adjustable to a desired reference value and is actuated by an actuating rod 1 projecting axially from the temperature sensing device, the non-illustrated control valve being adapted to act on the actuating rod 1 with a biassing force, which tends to displace the actuating rod 1 into the temperature sensing device.

In the very simple embodiment shown in figure 1, the tempera¬ ture sensing device comprises a massive, cylindrical housing 2 of a polymer material, the actuating rod 1 projecting axially from one end of the housing in a central, cylindrical cavity 3, and the other end of the housing adjoining a cup-shaped casing 4 of a heat conducting polymer material, e.g. a polyolefine, wherein a closed chamber 5 is formed between the inside of the casing 4 and the massive, heat insulating housing 2.

The housing 2 has a sleeve portion 6 projecting axially towards the casing 4 and being enclosed by the diaphragm 7 of an elastically stretchable material, in particular a ther o- elastomer. At the radially outer portion, the diaphragm 7 has a radially projecting flange 7a which is sealingly fitted between a shoulder 4a and a ring member 8, which encloses the sleeve portion 6 and is likewise made of a polymer material. From the flange 7a and an adjoining lip 7b, which engages with the inside of the casing 4, the diaphragm 7 extends radially inwardly while engaging with the ring 8 and merges, via a rounded portion, with an axially extending portion 7c, which engages with the outside of the sleeve portion 6 of the housing 2. The sleeve portion 6 has a rounded edge portion 6a, and the diaphragm follows this edge portion with a rounded portion 7d, which merges with a planar portion 7e into a central portion 7f, which is kept in engagement with the end surface 9a of a piston 9 being slidable in the cylindrical cavity 3. The inner end la of the actuating rod 1 is fitted into a central recess 9b in the opposite end of the piston 9.

As appears from figure 1, the closed chamber 5 consists of an annular portion 5a located radially outwardly of the sleeve portion 6 and the portion 7c of the diaphragm, and a central portion 5b between the planar portion 7e, 7f of the diaphragm and the end portion 4b of the casing 4.

The closed chamber 5 is prefilled with a wax-like material or a fluid, e.g. an organic ester having a high coefficient of volume expansion, so that when the temperature in the ambient air outside the casing 4 increases, heat will be transferred through the heat conducting material of the casing 4 into the fluid, whereupon the. fluid will expand and exert an increasing pressure on the diaphragm 7. Upon being exposed to such an increasing pressure, the central portion 7f of the diaphragm will displace the piston 9 and the actuating rod 1 to the left in figure 1, against the action of a biassing force generated by the non-illustrated control valve. When the piston 9 is displaced to the left, the central portion 7f of the diaphragm will reach the plane defined by the planar portion 7e of the diaphragm and thereafter be stretched inwardly into the cavity 3 while continuously engaging with the end surface 9a of the piston 9. Since the central portion 7f of the diaphragm 7, in the illustrated embodiment, will be stretched in opposite directions in the initial stage, at a low temperature, and in the final stage, at higher temperatures, respectively, the stretchability of the diaphragm material will be used in the best possible way for achieving as large a stroke as possible for the piston 9 when the latter is being displaced within its operational region.

The heat transfer from the outside of the casing 4 to the wax or the fluid in the chamber 5 will be particularly good in case the casing 4 is provided at the inside thereof with circum- ferentially distributed, axially extending grooves 10, which significantly enlarges the effective area of the boundary surface between the casing material and the wax or the fluid. The grooves 10 may alternatively be formed as inwardly projecting ridges or flanges. The essential point is that the inside of the casing has a large effective area. On the drawings only one groove 10 is shown. In practice, a plurality of such grooves are distributed circumferentially.

When manufacturing the temperature sensing device according to figure 1, the various parts are injection moulded from a polymer material, the diaphragm 7 and the ring 8 possibly being produced by double moulding. Alternatively, the ring 8 and the diaphragm 7 are joined together after the injection moulding, e.g. by ultrasonic welding. The unit consisting of the diaphragm 7 and the ring 8 is thereafter joined to the casing 4 in a suitable manner, e.g. by welding or gluing. Thereafter, the chamber 5 is filled with wax or fluid by inserting two fine needles through a plug 7g projecting axially through the ring 8. The fluid is fed through one of the needles, whereas air is evacuated through the other one. Thereafter, the holes for the needles are closed, and the unit consisting of the ring 8, the diaphragm 7 and the casing 4 is joined to the housing 2, e.g. by gluing. Finally, the piston 9 and the actuating rod 1 are inserted into the central cavity 3. The second embodiment of the temperature sensing device according to the invention, illustrated in figures 2a, 2b and 2c, differs from the one described above in that the sleeve portion 6 of the housing 2 is replaced by a separate sleeve 6' , which is axially displaceable in a widened, central cavity 3 ' and which guides the piston 9 and the actuating rod 1 in a corresponding manner as in figure 1. The sleeve 6' is biassed towards the position shown in figure 2a by means of a strong pressure spring 11, one end of which abuts the end wall of the housing 2 and the other end of which is inserted into an annular recess 12 in the sleeve 6 ' and abuts the bottom of the recess 12 adjacent to the end of the sleeve 6' engaging with the diaphragm. A radially projection flange 6 'a engages with a stop shoulder 8a on the ring 8 and holds the sleeve 6 ' in a well-defined position as shown in figure 2a.

When the temperature rises and the wax or the fluid in the chamber 5 is expanded, the central portion 7f of the diaphragm 7 will displace the piston 9 and the actuating rod 1 to the left, as illustrated in figure 2b. In this process, the sleeve 6' is still held in its end position to the right because of the action of the strong spring 11. It will be evident that the central portion 7f of the diaphragm 7 is then stretched considerably while being engaged with the end surface of the piston 9, and the stretched, central portion 7f of the diaphragm will then be substantially thinner.

Upon a further temperature increase, e.g. to temperatures around 100°C or more, the wax or the fluid in chamber 5 will be further expanded and will exert a great pressure force on the whole diaphragm 7. The possible further movement of the piston 9 to the left is limited, and upon an increasing pressure force on the diaphragm 7, the sleeve 6' will instead be displaced axially to the left against the action of the spring 11. Figure 2c illustrates how the sleeve 6' is displaced to the left, and the diaphragm 7 follows the sleeve under the influence of the fluid pressure in the chamber 5. In spite of the increasing pressure, the stretching of the diaphragm 7 is reduced because the end surface of the sleeve 6 ' facing the casing 4 is located closer to the ring 8 and the piston 9.

Accordingly, the second embodiment according to figures 2a, 2b and 2c has an inherent safety function which ensures that the diaphragm 7 is kept intact even at very high temperatures.

The unit formed by the ring 8, the diaphragm 7 and the casing 4 is exactly alike in the two shown embodiments according to figure 1 and figures 2a-2c, respectively.

Claims

1. Temperature sensing device adapted to bring about an actuating movement of a control valve for a heating medium, comprising a housing (2) with a closed fluid chamber (5), which is filled with a fluid having a high coefficient of volume expansion and which is enclosed externally by a heat conducting casing (4) and internally by an elastically stretchable dia¬ phragm (7) abutting an axially movable actuating means (9, 1) in order to bring about said actuating movement during tempera¬ ture variations in the ambient region of said casing, c h a r a c t e r i z e d i n that said housing (2) is made of a heat insulating material, whereas said casing (4) is made of a plastics material having a good thermal conductivity, said axially movable actuating means (9, 1) comprises a piston (9), which is slidable in a sleeve body (6, 6') in said housing (2) , said sleeve body protruding axially towards said casing (4) , - said piston and the surrounding sleeve body (6, 6') form a continuous abutment surface for said diaphragm (7), said piston (9) is movable in an operational region adjacent to the end surface of the sleeve body (6, 6'), said operational region being limited by an inner end position located inside said end surface, while being influenced by the volume expansion of the fluid during normal temperature variations, wherein the central portion (7f) of the diaphragm (7) continuously abuts the end surface of the piston (9) and follows the movements of the piston while being stretched.

2. Temperature sensing device as defined in claim 1, wherein the inside of the casing (4) is provided with flanges, ridges or grooves (10) for enlarging the heat transferring boundary surface between the plastics material and the temperature sensitive fluid.

3. Temperature sensing device as defined in claim 1 or claim 2, wherein the radially outermost portion (7a, 7b) of the diaphragm extends all the way to said casing (4) and engages sealingly at the inside thereof.

4. Temperature sensing device as defined in claim 3, wherein the radially outermost portion (7a) of the diaphragm engages with an annular member (8) enclosing said sleeve body (6, 6').

5. Temperature sensing device as defined in any one of claims 1 through 4, wherein said sleeve body (6, 6') has a rounded edge portion (6a) .

6. Temperature sensing device as defined in any one of claims 1 through 5, wherein each one of said housing (2), said casing (4), said sleeve body (6, 6'), said annular member (8) and said piston (9) is made of plastics material.

7. Temperature sensing device as defined in any one of claims 1 through 6, wherein said sleeve body (6) is made in one piece with said housing (2) .

8. Temperature sensing device as defined in any one of claims 1 through 6, wherein said sleeve body consists of an axially movable sleeve (6¹), which is biassed by a safety spring (11) , the spring force of which will only be surpassed at an elevated pressure in said fluid chamber, wherein said sleeve (6') is axially displaced whereas the piston (9) maintains its position.

9. Temperature sensing device as defined in any one of the preceding claims, wherein the piston (9) acts on said control valve by means of an actuating rod (1) , which is biassed towards said diaphragm (7) .