GB2032184A

GB2032184A - Thermostats

Info

Publication number: GB2032184A
Application number: GB7932808A
Authority: GB
Original assignee: Texas Instruments Italia SRL
Current assignee: Texas Instruments Italia SRL
Priority date: 1978-09-22
Filing date: 1979-09-21
Publication date: 1980-04-30
Also published as: DE2938005A1; IT1157192B; FR2437055A1; IT7851211A0

Abstract

A thermostat has two switching temperatures and includes two bimetallic discs 8 and 9 each of which is adapted to move a movable contact arm 13 by exerting a force on an interposed force transmitting cylinder 18. Each bimetallic disc is associated with two strip-like fixed terminals 15 and 17 which are slid into a cavity 10 in a resilient plastics body 1 of the thermostat deforming the plastics material against its resilience and thereby retaining them in position. The fixed terminals 15 and 17 and the bimetallic discs 8 and 9 extend parallel to the longitudinal axis of the thermostat. <IMAGE>

Description

SPECIFICATION Thermostats The present invention relates to thermostats, and in particular to those thermostats which are switched at two or even more different temperatures.

A known type of thermostat having two switching temperatures includes a generally cylindrical body and two dished bimetallic discs extending transverse to the thermostat axis and each mounted to actuate a respective movable contact arm by means of a respective interposed force transmitting cylinder. The two bimetallic discs and the force transmitting cylinders are coaxially arranged, and it is therefore necessary firstly that one of the discs has a hole in it through which the force transmitting cylinder associated with the other disc extends, and secondly that one of the force transmitting cylinders is hollow and slidably accommodates the other within it. As well as being complex this construction has the disadvantage that its switching temperatures must be accurately calibrated.

It is an object of the present invention to provide a thermostat of simplified construction, which does not require calibration after assembly and may be easily mounted in its operative position and particularly a thermostat having two or more switching temperatures.

According to the present invention there is provided a thermostat having a plastics body in which two fixed terminals are secured including a thermally responsive member, a movable contact electrically connected to one of the fixed terminals and mounted to be movable between a first position in which it is in electrical contact with the second fixed terminal and a second position in which it is not, and biassing means urging the movable contact member towards one of the said positions, the thermostat being constructed and arranged so that at a predetermined temperature the thermally responsive member urges the movable contact from one of the said positions to the other, the plastics material being resilient and deformed by the two fixed terminals and secured in position by the resilience of the plastics material.The preferred embodiment includes two thermally responsive members, e.g. dished bimetallic discs, each associated with a respective pair of fixed terminals, a movable contact and biassing means, the two thermally responsive means being arranged to actuate their respective movable contact at different predetermined temperatures.

The or each thermally responsive member is preferably associated with a force transmitting member interposed between it and the respective movable contact. Force transmitting members, e.g. cylindrical pins, of standard size may be used without individual adjustment resulting in a reduction of production costs.

Further features and details of the invention will be apparent from the following description of certain specific embodiments which is given by way of example with reference to the accompanying drawings, in which: Figure 1 is a plan view, partially in section, of a thermostat in accordance with the invention; Figure 2 is an elevation sectioned on two different planes of the thermostat of Figure 1; Figure 3 is a sectional elevation in a direction perpendicular to that of Figure 2; Figures 4a and 4b are scrap views from the front and side respectiveiy of one movable contact arm of the thermostat; Figures 5 and 6 are diagrammatic drawings of two modified constructions secured to the wall of a receptacle; and Figure 7 is an exploded diagrammatic perspective view of the more important components of a thermostat in accordance with the present invention.

The thermostat has a body 1 of resilient plastics material within a metal casing 2 which has an external rim or flange 3. The body and casing are of generally cylindrical form but have two diametrically opposed flat portions, those of the casing being designated 4 and 5. Adjacent the flat portions 4 and 5 the body affords a respective recess 6 and 7 which constitute seatings for a respective bimetallic disc 8 and 9 of domed or dished type whose direction of curvature reverses when a predetermined temperature is reached.

The two discs are constructed to reverse their curvature at different predetermined temperatures.

Only the right hand half of the thermostat as seen in Figure 1 will be described since the construction of the other half is identical.

The body 1 affords a cavity 10 which accommodates a movable contact arm 13 carrying a contact pad 13' at one end, and a fixed contact pad 1 4 secured to an elongate strip-like fixed terminal 1 5. The contact arm 13, whose structure is best seen in Figures 4a and 4b, includes a spring 1 6 and is permanently connected to a second fixed terminal 1 7 similar to that designated 1 5.

In the position shown in Figure 1 the connectors 1 5 and 1 7 are in electrical contact through the spring 16, arm 13 and fixed contacts 13' and 14, and this is the normal position of the thermostat. In contact with the bimetallic disc 8 is a force transmitting cylinder 1 8 which is urged by the bimetallic disc, when it changes its curvature, into contact with a protuberance 1 9 on the spring 16 thus moving the contact 13' on the end of the arm 1 3 out of engagement with the fixed contact 14.It will be noted that the spring 1 6 is provided with a supplementary elastic arm 20 integral with it positioned between the cylinder 1 8 and protuberance 1 9 which substantially eliminates vibration and noise on actuation of the thermostat by the cylinder 18 and by the bimetallic disc 8 which is practically floating in its seat. The arm 20 also remains in contact with the cylinder 18 at all times and urges it into contact with the disc 8.

It will be appreciated that the thermostat contacts may be readily converted to a state in which they are normally opened by merely reversing the orientation of the bimetallic disc 8.

It will be appreciated that the thermostat contacts may be readily converted to a state in which they are normally open by merely reversing the orientation of the bimetallic disc 8.

As may be seen in Figures 2 and 3 the thermostat is covered by a lid 24 which is held in position by two catches 26 and 27 which are formed integrally with the body, and each have a projection, giving it the appearance of a ratchet, which engages the upper surface of the lid. As may also be seen in Figure 2 the cylinder 18 passes through an open-topped slot and is held in position by a tongue 23 integral with the lid. The bimetallic disc is also vertically restrained by a projection 25 integral with the lid 24, but nevertheless remains free or floating within the recess 6.

The terminal 1 5 is provided with laterally projecting teeth 21, and when it is positioned in the body by sliding it in, the teeth deform or bite into the plastic material against its resilience and thus secure the terminal in position. The terminal 1 7 also has similar teeth to hoid it in position. In addition, as may be seen from Figure 1, the body 1 is provided with two additiona! cavities 11 adjacent the terminal 1 7 which together with the cavity 10 define a T section web whose head 37 is deformed by and engages the terminal 17 and also serves to secure it in position. Similarly a cavity 12 adjacent the terminal 1 5 defines with the cavity 10 two projections 38 which are also deformed by and engage the terminal 1 5.It will be appreciated that the terminals may be secured by teeth alone, or by deformation of one or more webs alone or by other means which result in the deformation of the plastics material.

Figure 3 shows one way of mounting the thermostat on the wall of a receptacle, part of which is shown at 28, by means of an annular trim 29 made of rubber having a slot in which the flange 3 of the metal casing 2 engages.

In the embodiment shown in Figure 5 the structural part of the thermostat is made entirely from plastics material. The body 30 has seats provided for the bimetallic discs in thinner regions of the body 30 indicated by a broken line at 31.

Several wedge-shaped segments 32 with an inciined ramp surface 33 are formed on the body 30. The wedge-shaped segments 32 enter correspondingly shaped openings in the wall of a receptacle designated 34 so as to form a bayonet assembly so that the upper rim 35 of the body 30 can compress an annular trim 36 against the outer wall of the receptacle 34 so as to ensure the necessary seal.

In the embodiment shown in Figure 6 the structural part of the thermostat is again made entirely of plastics material. The body 40 has seats provided for the bimetallic discs in thinner regions of the body 40 indicated by a broken line at 41. On the body 40 are formed several threads 42, interrupted at the regions 41 and intended to engage by screwing in a corresponding opening arranged in a wall 43 of the receptacle. Sealing is ensured by the annular trim 44 which is retained between the outer wall of the receptacle 43 and the upper rim 45 of the body of the thermostat.

In both these embodiments the operation of mounting the thermostat on the receptacle is considerably simplified by comparison with that shown in Figure 3.

Figure 7 is an exploded view of the principal elements of the thermostat according to the present invention. This figure shows the structure of the body 1 with the recesses 6, 10, 11, 12 and the elements 8,18,14,13,19,20,15,17 identified above. It is not thought necessary to give a further detailed description of the different elements.

The terminals 1 5 and 1 7 with the associated contact arm 13 may simply be slid into the cavities in the body 1 and then retained in position by virtue of the deformation of the plastics material. Thus no separate action is required to secure the terminals such as bending as otherwise deforming them.

It should be noted that, as described above, the thermostat according to the present invention has a modular structure which makes it possible for the assembler to reduce the number of items in stock and that the bimetallic discs and the other elements extend parallel to the axis of symmetry, in comparison to known constructions in which these discs and the other elements are perpendicular to the axis of symmetry (i.e. parallel to the end surfaces of the receptacle).

Claims

Claims

1. A thermostat having a plastics body in which two fixed terminals are secured including a thermally responsive member, a movable contact electrically connected to one of the fixed terminals and mounted to be movable between a first position in which it is in electrical contact with the second fixed terminal and a second position in which it is not, and biasing means urging the movable contact member towards one of the said positions, the thermostat being constructed and arranged so that at a predetermined temperature the thermally responsive member urges the movable contact from one of the said positions to the other, the plastics material being resilient and deformed by the two fixed terminals and secured in position by the resilience of the plastics material.

2. A thermostat as claimed in Claim 1 including two thermally responsive members, each associated with a respective pair of fixed terminals, a movable contact and biassing means, the two thermally responsive means being arranged to actuate their respective movable contact at different predetermined temperatures.

3. A thermostat as claimed in Claim 1 or Claim 2 in which the or each thermally responsive member is associated with a force transmitting member interposed between it and the respective movable contact.

4. A thermostat as claimed in Claim 3 in which the or each movable contact is connected to an elastic element arranged to remain in contact with the respective force transmitting member.

5. A thermostat as claimed in any one of the preceding claims in which the or each thermally responsive member is a dished bimetallic disc.

6. A thermostat as claimed in Claim 5 when dependent on Claim 2 in which the fixed terminals are elongate and both they and the bimetallic discs extend parallel to the axis of symmetry of the thermostat.

7. A thermostat as claimed in any one of the preceding claims in which the or each thermally responsive member is arranged externally of the plastics body.

8. A thermostat as claimed in any one of the preceding claims in which at least one of the fixed terminals is provided with teeth which deform the material of the body against its resilience thus securing the fixed terminal in position.

9. A thermostat as claimed in any one of the preceding claims in which at least one of the fixed terminals is received in a cavity in the body adjacent which is one or more further cavities which define at least one web, which is deformed by and bears against the fixed terminal thus securing it in position.

10. A thermostat as claimed in any one of the preceding claims in which the body is covered by a lid retained in position by two catches formed integrally with the body which engage the upper surface of the lid.

11. A thermostat as claimed in any one of the preceding claims including an outer metallic casing having an external flange by means of which the thermostat may be secured to the wall of a receptacle.

12. A thermostat as claimed in any one of Claims 1 to 10 in which the body is provided with screw threads adapted to threadedly secure it to the wall of a receptacle.

14. A thermostat substantially as specifically herein described with reference to Figures 1 , 2, 3, 4a, 4b and 7 or Figure 5 or Figure 6 of the accompanying drawings.