MCWILLIAMS, Kevin Ronald (12 Broad Walk, Stratford-upon-Avon, Warwickshire CV37 6HS, GB)
CLAIMS
1. A temperature sensor for a radiant electric heater, the sensor comprising:
a switch housing (7);
a first expansion element (3) secured at one end thereof to the housing;
a second expansion element (5) mounted at its free end with a free end of the first expansion element such that the free ends of the two elements are immovable relative to each other, the first and second expansion elements having different coefficients of thermal expansion;
a snap switch (11 ) disposed within the housing and including a switch arm (9); and
a resilient assembly (21 ) disposed in the housing and engaging directly with the switch arm so as to urge the switch arm against the end of the second expansion element.
2. A temperature sensor as claimed in claim 1 , characterised in that the first expansion element (3) is in the form of a tube and the second expansion element (5) is in the form of a rod arranged within the tube.
3. A temperature sensor as claimed in claim 1 or 2, characterised in that the first expansion element (3) is made of a metallic material.
4. A temperature sensor as claimed in claim 3, characterised in that the second expansion element (5) is selected from a ceramic, glass, and metal having lower thermal expansion that the first expansion element (3).
5. A temperature sensor as claimed in any preceding claim, characterised in that the switch arm (9) includes an articulation point (19) in the form of a deformation extending towards the other end of the second expansion element (5) so as to contact the same and the resilient assembly (21 ) includes means
5 protruding towards and engaging within the deformation of the switch arm so as to urge the articulation point against the end of the second expansion element.
6. A temperature sensor as claimed in claim 5, characterised in that the deformation (19) is substantially V-shaped with the apex thereof extending 0 towards and engaging with the end of the second expansion element (5).
7. A temperature sensor as claimed in any preceding claim, characterised in that the resilient assembly (21 ) includes a spring element (23) having a portion extending substantially in the axial direction of the second expansion element 5 (5).
8. A temperature sensor as claimed in claim 7, characterised in that the spring (23) comprises a flat spring with the axial portion (25) thereof being narrower than the remainder thereof. 0
9. A temperature sensor as claimed in claim 7 or 8, characterised in that the spring element (23) is substantially C-shaped.
10. . A temperature sensor as claimed in any one of claims 1 to 8, '5 characterised in that the resilient assembly (21 ) includes a spring element (29,
37, 41 ) mounted with the switch arm (9) of the snap switch (11 ) and with a carrier (27) for a reaction arm (13) of the snap switch such that the three components are co-located in the housing (7).
0 11. A temperature sensor as claimed in claim 10, characterised in that the three components (13, 27, 29, 37, 41) are formed as a separate assembly for mounting in the housing (7).
12. A temperature sensor as claimed in claim 10 or 11 , characterised in that the spring element (29) is located primarily on that side of the reaction arm (13) of the snap switch (11 ) remote from the switch arm (9), an end portion of the spring element passing through the carrier (27) for engagement in an articulation point (19).
13. A temperature sensor as claimed in claim 10 or 11 , characterised in that the spring element (29, 37, 41) is located intermediate the carrier (27) and the switch arm (9).
14. A temperature sensor as claimed in claim 13, characterised in that the resilient assembly (21) is secured at one end thereof to the switch arm (9) of the snap switch (11 ).
15. A temperature sensor as claimed in claim 14, characterised in that the resilient assembly (21) is secured by means of a rivet (39).
16. A temperature sensor as claimed in claim 14 or 15, characterised in that the securing means (39) is positioned between the switch arm (9) and the end of the second expansion element (5).
17. A temperature sensor as claimed in any one of claims 14 to 16, characterised in that the resilient assembly (21) comprises a strip-form spring (37, 41).
18. A temperature sensor as claimed in claim 17, characterised in that the strip-form spring (37) runs substantially alongside the switch arm (9).
19. A temperature sensor as claimed in claim 17, characterised in that the strip-form spring (37) is spaced from the switch arm (9) intermediate the ends of the spring.
20. A temperature sensor as claimed in claim 5 or 6, characterised in that the spring element (31 ) of the resilient assembly (21 ) is in the form of a V with free ends. (33) of the spring element engaging in a carrier (27) and an apex (35) engaging in the deformation (19) of the articulation point.
21. A temperature sensor as claimed in claim 20, characterised in that the free ends (33) of the spring element (31 ) engage in a rectangular formation of the carrier (27). |
TEMPERATURE SENSOR FOR RADIANT ELECTRIC HEATERS
This invention relates to a temperature sensor for a radiant electric heater.
Temperature sensors for radiant electric heaters, especially those used in cooking hobs, generally comprise a differential expansion member which is connected to a housing in such a manner that an element of the differential expansion member is adapted to operate a snap switch as a result of expansion and contraction of the differential expansion member.
Such a temperature sensor is described in US-A-20050184849 in which the expansion member comprises a metal tube enclosing a rod of ceramic material, the two elements being secured together in the region of the ends thereof remote from a housing. The tube is secured in the housing such that expansion and contraction of the expansion member results in axial movement of the rod within the housing. An arm of a snap switch is clamped between the end of the rod and a resilient assembly so as to reduce the risk of early failure of the snap switch as a result of fatigue. The resilient assembly acts in the axial direction of the rod and comprises a coil spring which extends around a support which acts on the arm of the snap switch by way of a spring plate.
A disadvantage of this arrangement is that the coil spring, the support and the spring plate are all guided by a buttress within the housing or by a carrier for a further arm of the snap switch. In each case, the need to support the components of the resilient assembly gives rise to friction between the resilient assembly and its support. Such friction can give rise to unreliable switching.
A further disadvantage of the prior art arrangement is that the support for the coil spring is positioned between the coil spring and the arm of the snap switch and can therefore lead to switching at inaccurate temperatures.
It is therefore an object of the present invention to provide a temperature sensor which overcomes or at least ameliorates at least one of the above disadvantages.
According to the present invention there is provided a temperature sensor for a radiant electric heater, the sensor comprising:
a switch housing;
a first expansion element secured at one end thereof to the housing;
a second expansion element mounted at its free end with a free end of the first expansion element such that the free ends of the two elements are immovable relative to each other, the first and second expansion elements having different coefficients of thermal expansion;
a snap switch disposed within the housing and including a switch arm; and
a resilient assembly disposed in the housing and engaging directly with the switch arm so as to urge the switch arm against the end of the second expansion element.
The first expansion element may be in the form of a tube and the second expansion element may be in the form of a rod arranged within the tube.
The first expansion element may be made of a metallic material. The second expansion element may be made of a ceramic, glass or metal having lower thermal expansion that the first expansion element.
The switch arm may include an articulation point in the form of a deformation extending towards the other end of the second expansion element so as to contact the same and the resilient assembly may include means protruding
towards and engaging within the deformation of the switch arm so as to urge the articulation point against the end of the second expansion element.
The deformation may be substantially V-shaped with the apex thereof extending towards and engaging with the end of the second expansion element.
The resilient assembly may include a spring element having a portion extending substantially in the axial direction of the second expansion element. The spring may be a flat spring with the axial portion thereof being narrower than the remainder thereof. The spring element may be substantially C-shaped.
The resilient assembly may include a spring element mounted with the switch arm of the snap switch and with a carrier for a reaction arm of the snap switch such that the three components may be co-located in the housing. The three components may be formed as a separate assembly for mounting in the housing. The spring element may be located primarily on that side of the reaction arm of the snap switch remote from the switch arm, an end portion of the spring element passing through the carrier for engagement in the articulation point. Alternatively, the spring element may be located intermediate the carrier and the switch arm.
The resilient assembly may be secured at one end thereof to the switch arm of the snap switch, for example by means of a rivet. The securing means may be positioned between the switch arm and the end of the second expansion element. The resilient assembly may comprise a strip-form spring. The strip- form spring may run substantially alongside the switch arm or may be spaced therefrom intermediate the ends of the spring.
As a further alternative, the spring element of the resilient assembly may be in the form of a V with free ends of the spring element engaging in a carrier, for example in a rectangular formation of a carrier, and an apex engaging in the deformation of the articulation point.
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For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which:
Figure 1 is a diagrammatic illustration of one embodiment of a temperature sensor according to the present invention;
Figure 2 is a diagrammatic illustration of part of a modification of the temperature sensor of Figure 1 ;
Figure 3 is a perspective view of a resilient assembly forming part of the temperature sensor of Figure 2;
Figure 4 is a diagrammatic illustration of part of a further modification of the temperature sensor of Figure 1 ;
Figure 5 is a diagrammatic illustration of part of another modification of the temperature sensor of Figure 1 ;
Figure 6 is a diagrammatic illustration of part of a yet another modification of the temperature sensor of Figure 1 ;
Figure 7 is a diagrammatic illustration of part of a further modification of the temperature sensor of Figure 1 ;
Figure 8 shows a spring element forming part of the modification of Figure 7; and
Figure 9 is a diagrammatic illustration of a modification of the temperature sensor part shown in Figure 7.
The temperature sensor shown in Figure 1 comprises a differential expansion member 1 in the form if two elongate expansion elements 3, 5 which have
significantly different coefficients of thermal expansion. In particular, expansion element 3 may comprise a tube of metallic material of relatively high coefficient of thermal expansion, while expansion element 5 may comprise a rod of ceramic material of relatively low coefficient of thermal expansion.
The free ends of the expansion elements 3 and 5 are mounted together in such a manner that they cannot move relative to each other. The other end of the expansion element 3 is secured within a housing 7, while the other end of the expansion element 5 is free to move. Consequently the ends of the differential expansion member within the housing 7 move relative to each other, in the axial direction of the member 1 , as the expansion member is heated and cooled, with the result that the end of the rod-form expansion element 5 moves outwardly relative to the housing as the expansion member is heated and moves inwardly relative to the housing as the expansion member is cooled.
The end of the rod-form expansion element 5 within the housing 7 bears against an actuating arm 9 of a snap switch 11 , the snap switch also including a reaction arm 13 which creates the snap effect of a contact 15. Contact 15 makes or breaks with a counter contact 17 so as to control the supply of electrical power to a radiant electric heater of which the temperature sensor forms a part in a manner well known to the skilled person. The reaction arm 13 is supported in a carrier 27 which is mounted in the housing 7.
At the point where the actuating arm 9 of the snap switch bears against the end of the rod-form expansion element 5, the actuating arm is formed with an articulation point 19 in the form of a substantially V-shaped deformation with the apex of the deformation being directed towards and bearing against the end of the rod-form expansion element 5.
The actuating arm 9 of the snap switch is urged against the end of the rod-form expansion element 5 by means of a resilient assembly 21 in the form of a generally C-shaped spring element 23 which incorporates a switch-engaging
portion 25 extending substantially in the axial direction of the differential expansion member 1 and engaging in the substantially V-shaped deformation so as to clamp the actuating arm of the snap switch between the end of the rod- form expansion element 5 and the resilient assembly 21.
Thus, the free end of the switch-engaging portion 25 of the resilient assembly 21 is restrained from movement by the substantially V-shaped deformation of the articulation point 19 and requires no further support which could introduce friction and render the switching operation of the snap switch 11 unreliable.
Figures 2 and 3 show a modification of the temperature sensor of Figure 1 , in particular in relation to the configuration of the resilient assembly 21. The same references are used in Figures 2 and 3 to denote the same or similar components. The C-shaped spring 23 in Figures 2 and 3 is reversed compared with that in Figure 1 , but Figure 3 shows that the switch-engaging portion of the spring which engages with the substantially V-shaped deformation of the articulation point is narrowed at each side compared with the width of the flat spring 23.
Figure 4 shows a modification ofthe temperature sensor of Figure 1 , in particular in relation to the configuration of the resilient assembly 21. The same references are used in Figure 4 to denote the same or similar components. The spring 29 in Figure 4 is mounted in the housing 7 at the same location as the switch actuating arm 9 and the carrier 27 for the reaction arm 13. Such an arrangement permits pre-assembly ofthe snap switch together with the resilient assembly 21 in a single step rather than assembling the snap switch and the resilient assembly in the housing in two steps.
Figure 5 shows a further modification of the temperature sensor of Figure 1 , in particular in relation to the configuration ofthe resilient assembly 21. The same references are used in Figure 5 to denote the same or similar components. The modification of Figure 5 is similar to that of Figure 4 in that the spring 29 is
mounted in the housing 7 at the same location as the switch actuating arm 9 and the carrier 27 for the reaction arm 13. However, in the case of Figure 5, the carrier 27 for the reaction arm 13 is located outside the spring 29 forming the resilient assembly, whereas in Figure 4 the spring 29 is primarily positioned externally of the carrier 27 and passes through the carrier to engage with the actuating arm 9.
Figure 6 shows another modification of the temperature sensor of Figure 1 , in particular in relation to the configuration of the resilient assembly 21 and the carrier 27. The spring 31 in Figure 6 is mounted in the housing 7 within the carrier 27 for the reaction arm 13, the spring being in the form of a broad V- shape with the free ends 33 of the spring engaging in corners of a rectangular recess formed in the carrier 27 and the apex 35 engaging in the substantially V- shaped depression of the articulation point 19 so as to urge the actuating arm 9 of the snap switch against the end of the rod-form expansion element 5. As with the embodiments of Figures 4 and 5, the arrangement permits pre-assembly of the snap switch together with the resilient assembly 21 in a single step rather than assembling the snap switch and the resilient assembly in the housing in two steps.
Figures 7 and 8 show an embodiment similar to Figure 6 in that the carrier 27 has a rectangular recess formed therein. However the resilient assembly 21 is in the form of a curved strip-form spring 37 which is sandwiched between the actuating arm 9 and the carrier 27 where the carrier and the actuating arm are mounted in the housing 7 and which is secured to the actuating arm by means of a rivet 39 or the like in the region where the actuating arm is adjacent to the end of the rod-form expansion element 5. The spring 37 urges the actuating arm 9 of the snap switch 11 against the end of the expansion element 5 by way of the rivet 39. The spring 37 is curved when in its free-standing configuration, but is straightened into a stressed configuration when in used and runs substantially alongside the actuating arm 9 when in use.
Figure 9 shows a modification of Figure 7 in that the curvature of spring 41 is such that the spring does not run alongside the actuating arm 9, but is spaced from the actuating arm between the ends of the spring.
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