EP0100861B1 - Electric cooking plate with a temperature-protected switchgear - Google Patents

Description

The invention relates to an electric hotplate with a hotplate body and a temperature circuit breaker arranged on its underside according to the preamble of claim 1.

Such a temperature limiter has become known from DE-C-1 123 059. This temperature limiter, which has been installed millions of times in hot plates, works extremely reliably and is particularly suitable for working as a relatively weak temperature limiter coupled to the heating temperature with a large switching hysteresis. It consists of a crescent-shaped insulating housing, in the recess of which a snap switch and a bimetal parallel to it are arranged and fixed in that they protrude into slots or openings. The housing is closed by a cover and the temperature limiter is arranged in the unheated central zone of the electric hotplate, partially surrounding the cast-on central bolt, with the cover facing downwards and snap switches and bimetal standing on the side.

From DE-B-1 615 258 and DE-C-1 127 007 temperature switches have become known which are arranged on the underside of the heated zone of an electric hotplate. They have lids with which the temperature sensor and switching mechanism are locked and secured.

DE-C 1 104 087 shows a temperature limiter arranged in the unheated middle zone of an electric hotplate, the housing recess of which is closed by a cover.

The object of the invention is to provide a temperature limiter which can be produced with even less manufacturing effort and the smallest possible dimensions and whose coupling characteristics to the hotplate are improved.

This object is achieved by the characterizing part of claim 1.

Thanks to the box-shaped housing that is open on one side, the bimetal is better coupled to the temperature to be monitored by both convection and radiation. It contributes to this if the temperature limiter designed for arrangement in the unheated central zone of the electric hotplate advantageously points with its open side in the horizontal direction, that is to say normally for heating. However, it can also be consciously changed in its coupling characteristics by another arrangement. It is also possible to change this coupling characteristic by the snap switch and the bimetal lying in a horizontal plane in the installed state, the coupling characteristic changing depending on whether the bimetal is facing the hotplate body or is arranged facing away.

The very small box-shaped housing not only has a very uncomplicated design and is therefore very easy to manufacture from the most commonly used ceramic material (steatite), but also has a very small mass, so that there is no fear that condensation will adhere to the housing Precipitation of moisture that could lead to leakage currents.

The end and side walls of the housing surrounding the opening of the recess project above the snap switch and the bimetal, preferably by 1 to 3 mm. This, together with the other features already described, enables the temperature limiter to be constructed without a cover.

According to a further feature of the invention, the carrier carrying the snap switch and the bimetal can be fixed by an automatic locking mechanism acting with limited longitudinal movement.

In one embodiment, in which the housing of the temperature protection switch is supported on the cover plate and the temperature protection switch is pressed in defined contact against a surface of the hotplate body in the unheated central zone, it is possible to dispense with the cover cap previously surrounding the temperature protection switch, which reduces the Manufacturing and assembly costs. The specific heat of the overall arrangement is also reduced, and a usually necessary insulating lead-through part for the connecting wires of the temperature protection switch through the cover cap can be omitted. Preferably, projections can be provided on the side of the housing containing the opening of the recess, said projections being pressed into contact with the surface of the hotplate body. On the edge surrounding the recess, three projections can preferably be formed, which in particular have a rounded and possibly conical shape. These have the task, on the one hand, to ensure a sufficient distance between the functional parts of the temperature protection switch arranged in the recess and the hotplate body, on the other hand to ensure a defined system and still ensure a certain ventilation of the temperature protection switch.

A perforated, cup-shaped cover part can advantageously be provided for the unheated central zone. Due to the narrow, lattice-shaped structure of the bowl, which is also grounded due to the grounding of the hotplate body, despite effective ventilation of the central zone, it forms such a complete electrical protection that a temperature sensor can be used whose switch housing is open at least on one side, whereby advantageously Temperature sensor of the temperature protection switch is arranged in the switch housing. Furthermore, the overall level of the temperature monitoring of the hotplate can be reduced somewhat in order to make do with a simpler and robust switch which is integrated with its temperature sensor. The temperature limitation still works perfectly, although at first glance it does not seem sensible to monitor the temperature level lower first before sensing it with a temperature limiter.

It is also proposed a hotplate in which the housing of the temperature protection switch on its side facing away from the hotplate is open and the switch parts inserted into recesses can be secured against falling out by at least one fixing part which at least partially covers these slots and can be inserted into recesses in the switch housing and which can be directly attached the cover plate or on the hotplate body. This makes it possible to dispense with the cap that normally surrounds the temperature protection switch, which of course leads to cost savings. In addition, the omission of the cover of the circuit breaker housing also leads to cost savings, especially when assembling the switch from individual parts. The fixing part has a lower mass than the previously known cover, which leads to cost savings from the material side and to a reduction in the specific heat of the housing. The fact that the cap can be dispensed with also makes it possible to dispense with an insulating grommet for the supply wires for the temperature protection switch.

• Fig. 1 einen schematischen Teilschnitt durch eine Kochplatte mit einem Temperaturschutzschalter,
• Fig. 2 eine vergrößerte Draufsicht auf einen Temperaturschutzschalter, in Fig. 1 von oben gesehen,
• Fig. 3 eine teilweise abgebrochene Unteransicht einer Kochplatte mit Abdeckteil,
• Fig. 4 einen Schnitt nach der Linie IV in Fig. 1,
• Fig. 5 einen Teilschnitt durch eine Kochplatte,
• Fig. 6 ein Detail eines Temperaturschutzschalters;
• Fig. 7 bis 9 teilweise perspektivische Ansichten von Festlegungsteilen,
• Fig. 10 und 11 Teilschnitte durch Schutzschaltergehäuse und Abdeckblech,
• Fig. 12 einen Längsschnitt durch einen Temperaturschutzschalter geschnitten nach der Linie XII in Fig. 13,
• Fig. 13 einen Schnitt nach der geknickten Schnittlinie XIII in Fig. 12,
• Fig. 14 einen Detailschnitt nach der Linie XIV in Fig. 13.
• Fig. 15 einen Querschnitt nach der Linie XV in Fig. 13 und
• Fig. 16 die Unteransicht einer mit dem Temperaturschutzschalter versehenen Kochplatte.

Features of preferred developments of the invention emerge from the subclaims and the description in connection with the drawings, the individual features being able to be implemented individually or in groups in the form of subcombinations in one embodiment of the invention. Embodiments of the invention are shown in the drawing and are explained in more detail below. Show it:

• 1 is a schematic partial section through a hotplate with a temperature protection switch,
• 2 is an enlarged top view of a temperature protection switch, seen from above in FIG. 1,
• 3 is a partially broken bottom view of a hotplate with cover,
• 4 shows a section along the line IV in FIG. 1,
• 5 shows a partial section through a hotplate,
• Fig. 6 shows a detail of a temperature protection switch;
• 7 to 9 are partial perspective views of fixing parts,
• 10 and 11 partial sections through the circuit breaker housing and cover plate,
• 12 shows a longitudinal section through a temperature protection switch cut along the line XII in FIG. 13,
• 13 shows a section along the kinked section line XIII in FIG. 12,
• 14 shows a detail section along the line XIV in FIG. 13.
• Fig. 15 is a cross section along the line XV in Fig. 13 and
• 16 shows the bottom view of a hotplate provided with the temperature protection switch.

The electric hotplate 2 shown in FIG. 1 has a hotplate body 1 made of cast material, preferably cast iron, with a heating ring area 11, which is closed towards the outside and inside by ring ribs 12, 13 projecting downwards. In the heating ring area there are electrical heating resistors which are embedded in the grooves of the hotplate body in the insulating material. Within the inner annular rib 12 there is an unheated central zone 14, in the middle of which there is a central eye 15 in the form of a downwardly projecting cast pin, into the threaded bore of which a fastening bolt 16 is screwed.

The underside of the electric hotplate is closed by a profiled cover plate 17 which, in the embodiment according to FIG. 1, rests on the lower edge of the annular outer edge 13, covers the entire underside of the hotplate and is pressed upwards by the bolt 16 and a nut 18 screwed thereon .

A temperature protection switch 19 is arranged in the unheated central zone 14. It is connected via supply wires 20 and is intended to switch off the heating or a part thereof when the hotplate assumes a temperature above its set limit temperature. It is desirable that the temperature protection switch responds with a certain delay, because it can be used in this way to switch off an increased parboiling power after it has responded, in order to then have sufficient boiling power.

The temperature protection switch 19 is shown enlarged in FIG. 2. It corresponds in its structure and function to that according to DE-PS 1 123 059, to which reference is made. The functional parts 3 of the temperature protection switch are arranged in a recess 25 of a housing 23 made of insulating material, such as steatite, and are fixed by inserting them into slots in the housing 23. It is a bimetal 4, which is attached to a carrier 30 inserted into a slot 31 and moves the spring tongue of a snap spring of a snap switch 5. The snap spring carries at one end a contact which cooperates with a fixed mating contact on a connecting bar 29 which, like a connecting bar 28 for supplying current to the snap spring, is inserted into slots 27 of the housing and thereby fixed. The top view of the housing is essentially crescent-shaped or could also be described as rectangular with a recess on one long side and roundings on the opposite long side.

As can be seen from FIGS. 1 and 2, three projections 8 are provided on the edge 6 of the housing surrounding the recess 25 on the upper side 7, to which the recess 25 has its opening, which are integrally formed with the housing 23 and none have a conical shape with a rounded tip.

From FIG. 1 it can be seen that the temperature protection switch 19 is arranged in the central zone in such a way that the central eye 15 lies in the region of the recess 9 on a long side of the housing, this side having a flattened portion that is flattened 10 in FIG lower surface 50 of the central zone 14 merges.

The cover plate 17 preferably has only one projection 51, which is designed as an inwardly pronounced bead of the cover plate and presses on the flat underside 52 of the housing 23. As a result, the projections 8 are defined and pressed firmly against the surface 50 of the hotplate body in the region of the central zone. The opening of the recess 25 is open at the top, but is covered at some distance from the surface 50 of the hotplate body and is thus protected against contact.

When the bolt 16 or the nut 18 is tightened, the temperature protection switch is thus pressed into contact with the hotplate body. To maintain this pressure, on the one hand, an elastic design of the cover plate contributes, which, however, could also be supported by a corresponding spring element and / or shape of the end plate or the projection 51. So you could imagine, for example, that the area around the projection is formed resiliently by slots in the cover plate.

In Fig. The Heizringbereich 11 is covered by a cover plate 17a down, which rests on the edges 12 and 13 and is centered with a bent portion 72 in the interior of the inner edge 12.

The temperature protection switch 19 is switched on via two connecting lines 74 in one of the circuits of the hotplate. The lines 74 are led out of the central zone by means of an arranged insulating bushing 75 opposite the temperature switch 19. The middle zone is covered by a cover part 76, which has the shape of a relatively flat bowl with a substantially flat bottom 77, an essentially cylindrical jacket 78 and an outwardly projecting support flange 79 at the end of the jacket region 78. This support flange 79 rests on a shoulder 80 of the cover plate 17a and presses it against the underside of the edge 12. The cup-shaped support part 76 is made of perforated sheet material of relatively large thickness, preferably over 0.8 mm. In the exemplary embodiment, the sheet material is 1 mm thick. In the present example, the sheet metal material has circular holes 88 which are arranged in any manner and whose diameter is only a few millimeters, the hole area preferably being one third to two thirds and particularly preferably over half the total area. Because of the production of the bowl from sheet metal material perforated before the bowl deformation, the holes are provided over the entire bowl surface, but form a relatively coherent surface in the area of the outer support flange 79 that there is a uniform pressing of the cover plate 17a on the edge 12 .

The cover part 76 is fixed by means of a nut 81 screwed onto the fastening bolt 16 and thus also secures the cover plate 17a.

The temperature switch 19 is open on one side, i.e. its bimetal and the current-carrying switch parts are not covered by a special insulating cover. In normal operation it is almost impossible that something could touch these live parts without simultaneously touching the grounding provided by the grid-shaped or perforated cover part.

5 corresponds to that of FIG. 1 except for the differences described below.

In the area of the temperature protection switch 19, the cover plate 17b is provided with a plurality of ventilation holes 22. Two fixing parts 24 are arranged between the housing 23 of the temperature protection switch 19 and the cover plate 17.

6 shows a detail on a larger scale of the housing 23 of a temperature protection switch 19b. Its housing 23 has three holes 26, which are used in conventional temperature protection switches to hold a cover on the housing from above. On the right in FIG. 1, a slot 27, through which a connecting element 28 of the switch 19b passes, is closed off by a fixing part 24. The fixing part 24 has on its underside a cylindrical pin which is inserted into the hole 26 shown in dashed lines. It therefore covers the connecting element 28, prevents the entire switch mechanism from inadvertently moving out of the housing and supports the temperature protection switch on the end plate or the hotplate body. To fix the left connection element 29 (FIG. 2) and the switch carrier 30, a common fixing element would be used in this case, which has a cylindrical projection in the hole 26 and at least one further projection in the left slot 27 or in the recess 31 would intervene for the switch carrier 30.

FIG. 1 shows a bottom view of a fixing element 24, which has a circular cylindrical extension 32 and a cuboid extension 33. It is placed on the housing 23 of the temperature protection switch 19 so that the neck 32 engages in the hole 26 and the neck 33 in the slot 27.

FIG. 8 shows the fixing element 24 according to FIG. 4. On the side of the fixing element opposite the lugs 32 and 33, a rib 34 is arranged, which creates a linear contact of the cover plate 17.

9 has on its underside 36 an elongated extension 37, which is as long as the fixing element, and a cylindrical extension 32 and a rib 34.

10, the housing 23 of the switch 19 lies flush against the underside 38 of the unheated central zone 14 of the hotplate. The connecting element 28 is inserted in a slot 27 which is open on one side. The fixing element 24 engages with its one shoulder 32 in the hole 26 and with its second shoulder 33 in the slot 27 above the connecting element 28 and is thereby secured against rotation. Above the fixing element 24, the cover plate 17b is arranged, which, as already mentioned, is screwed onto the central eye 15. It bears against the rib 34 of the fixing element 24. Due to this arrangement, when the installation position is reversed, all switch elements are secured against falling out and therefore do not have to be cemented in place.

In Fig. 11 it can be seen that a further fixing element 40 on its side facing away from the hotplate has, in addition to two ribs 34, a higher extension 41 which engages in an opening 42 in the cover plate 17. Because of the approach 41, 8 from above, easily determine whether the fixing element 40 is correctly positioned.

To the right of the opening 42 for the extension 41, the cover plate 17b has two slots 43, which were created by punching out and bending away.

A temperature protection switch 111 is shown in FIGS. It has a housing 113 made of ceramic insulating material, for example steatite, which has the shape of an elongated rectangular box with one long side open. Accordingly, the housing has two narrow end walls 115, 117, two side walls 119, 121 and a bottom 122, which delimit a recess 123, while the only remaining side is an open side 124.

A carrier 125 made of stiff sheet metal material is arranged in the recess 123 and extends along the side wall 121 and is supported thereon with a stamping 141. A short, strong bimetal 127 is attached to it in parallel by means of a spot weld 128, by means of which a movable counter bearing 129, which is designed as a flexible sheet metal strip with a one-sided bend, is also fastened. By turning an adjusting screw 143, which is accessible through an opening 144 in the side wall 121, the deflection of the movable counter bearing relative to the bimetal 127 and thus the basic setting of a snap switch 131 can be adjusted. This has a snap spring arm 133 stiffened by laterally edged parts, the center of which is punched out in the form of a tongue and forms a snap spring 130 which is supported in the counter bearing 129 under a pre-tensioned bend. At its free end, the snap spring arm carries a contact 134, while the other end is supported in a cutting edge bearing 135, which is provided on a bend 137 of the carrier 125. In order not to burden the cutting edge bearing 135 with the currents to be switched, a connecting wire 145 is welded to the snap spring arm 133 and to the carrier 125.

In order to allow the bimetal to work freely, the carrier 125 is offset in several stages and has at its one end 139 two outer, foot-like projections which lie in two recesses 147, one of which is open to the recess 123 and to the open side 124 while the other is undercut by an intermediate end wall portion 149 projecting towards the recess, so that the end 139, when it lies in the depression 147 facing the floor, prevents movement of the carrier in the direction of the open side 124. An opening 151 in the bottom area is provided only for manufacturing reasons in order to be able to produce the undercut recess 147 in a two-part form without cores and slides.

The other end 153 of the carrier forms an electrical connection lug for a connection line 155 which is welded to the connection lug.

The end 153 forms a narrow extension in the area of the base 122 and protrudes through a cutout 157 which breaks through the corner between the end wall 117 and the base 122 and thus forms an opening which is accessible from the end wall and the bottom and which has a height (transversely to the plane of the carrier 125) is substantially greater than the thickness of the carrier (by approximately 3 to 4 times).

The end of the carrier 125 located in the interior of the recess 123 forms a stop surface 159 which, in the installed state, lies opposite a securing surface 161 (see FIG. 14) which forms a step in the end wall 117. The securing surface can extend from the open side 124 to the cutout 157, to a height that corresponds approximately to the center of the cutout 157.

The contact 134 of the snap switch 131 is opposite a mating contact 163 which is attached to a mating contact carrier 164. This is inserted into a slot 165, which has a flat V-shaped shape as can be seen in FIG. 12 and thus fixes the correspondingly dimensioned counter-contact carrier 164 relatively securely and without play when it is inserted. The final securing takes place in that a connecting line 166 is welded to the section of the mating contact carrier 164 projecting outward beyond the base 122.

During manufacture, the entire functional unit consisting of carrier 125, bimetal 127 and snap switch 131 is pre-assembled. The short, strong, slightly tapered (FIG. 13) bimetal 127 is welded to the support together with the counter bearing 129, the snap spring arm 133 and the snap spring 130 are hooked in and the strand 145 is welded on. The mating contact carrier 164 is inserted into the slot 165 and then the previously described assembled unit is inserted into the recess 123, the end 153 first being inserted obliquely through the recess 157, in such a way that the Stop surface 159 of the carrier 125 in FIG. 12 or 14 is located above the securing surface 161. As a result, the carrier 125 can be pushed to the left in the figures so that the end 139 can be pivoted in the direction of the curved arrow 167 in FIG. 13 and the end 139 can still be freely moved by the projecting end wall part 149. When the carrier 125 is pushed into its position against the floor 122, one need only push the carrier 125 to the right, and the snap spring arm 133 presses the carrier 125 downward in FIGS. 12 and 14 so that the Stop surface 159 is opposite to the securing surface 161 and no longer permits displacement of the carrier 125 to the left, as a result of which the snap switch carrier is secured in the position shown in FIGS. 12 and 14. The final securing takes place in that when the connecting line 155 is welded on, it is pressed into the part of the cutout 157 which now remains above the end 153. For this purpose, the connecting line can be slightly bent.

13 and 15 it can be seen that the definition is such that the current-carrying unit carrier 125 / bimetal 127 / snap switch 131 is at a considerable distance from the open side 124, i.e. the end and side walls 115 to 121 protrude over these parts by an amount between 1 to 3 mm. Given the relatively small width of the recess (less than 10 mm), there is sufficient protection against contact, so that a cover projecting beyond the recess 123 is not necessary. However, this improves the thermal connectivity of the temperature limiter and lowers its already very low overall mass, which benefits its switching and leakage current behavior.

The snap switch adjusted by lifting the movable counter-bearing 129 relative to the bimetal 127 is actuated when the bimetal 127 in FIG. 12 has warmed upwards to such an extent that the snap point of the snap switch is reached. The contacts 134, 163 closed in the illustrated state are then opened.

16 shows the temperature limiter 111 in its arrangement on a hotplate 170. It is a cast hotplate with a heated ring area 171, where the temperature limiter 111 is arranged in the unheated central zone 172 surrounded by an edge 173. It lies there on one side of a cast-on fastening piece 174 with its open side 124 facing the edge 173 and thus pointing towards the heating. The connecting lines 155, 166 go directly to corresponding connecting pins which protrude from the ceramic investment in the heated ring area and lead to one or more of the heating resistors arranged in the heated ring area.

In its position shown in FIG. 16, the interior of the temperature limiter is freely accessible to the heat coming from the hotplate, both by radiation and by conduction and convection. The coupling can be changed by changing the position, for example arrangement such that the open side 124 faces the fastening socket 174. The temperature limiter is normally installed in a position in which the side 121 lies against the hotplate body, so that the bimetal is closer to it. The characteristics of the coupling can also be changed by turning (page 119).

Above all, it can be seen that the temperature limiter is particularly easy to manufacture. Its housing consists of a single ceramic piece that can be produced in a simple two-part form, on which only two parts are to be assembled, both of which can be fixed by simple insertion without the need for cementing or the like, namely the mating contact carrier and the preassembled actuating unit carrier / bimetal / snap switch . The only adjusting screw is easily accessible. The individual parts are fixed by welding the connection line, which is to be carried out anyway. Nevertheless, the temperature limiter is particularly versatile and its coupling (fast or sluggish) can be adjusted by simply turning around during assembly to meet different requirements. It has also been shown that the previously required covering of the central zone 172 of the hotplate by a separate cover can be dispensed with in this temperature limiter, without there being an increased risk of leakage current.

It is also advantageous that both connections 153, 164 are located in the area of a narrow side of the housing, so that the connection lines leading away from them are short and can extend side by side through a recess in edge 173.

Claims (15)

1. Electric hotplate with a hotplate body (1, 170) and a thermostat (19, 19b, 111) arranged on its bottom and having an insulating material casing, within whose casing area (25, 123) surrounded by a casing body (23, 113) and open on one side of the latter, in which are arranged a snap switch by inserting a temperature sensor in the form of a bimetallic element (4,127) with a support (30, 125) and a snap spring contact (5, 130, 134) of a switching unit on the one hand and an opposite contact unit (29, 163, 164) on the other, the support (30, 125) with the bimetallic element (4, 127) and the opposite contact unit being fixed by inserting in insertion openings (27, 31, 147, 157, 165) of the casing body (23, 113) which are open towards the opening of the casing area (25,123), characterized in that the casing area (25, 123) of the thermostat (19, 19b, 111) are arranged in cover-less, open manner in the fitted state and that in the area of the casing wall surrounding the opening of the casing area (25, 123) are provided insulating parts (8, 24, 35, 115, 117, 119, 121) projecting at right angles to the opening plane opposite to the switching unit (3, 125, 127, 129) and the opposite contact unit (29, 163, 164).

2. Electric hotplate according to claim 1, characterized in that the switching unit is a unit preassembled with the temperature sensor, its support (125) and the snap spring contact (130, 134), which is secured in its position adjacent to the open side (124) of casing body (113) by the insertion of support (125) in insertion openings (147, 157).

3. Electric hotplate according to claims 1 or 2, characterized in that the casing (23) of the thermostat (19) is supported on a cover plate (17) covering the underside of the electric hotplate and the thermostat (19) is pressed into clearly defined contact on a surface (50) of hotplate body (1) in the unheated central zone (14), preferably in the vicinity of a flattened portion (10) of hotplate body (1).

4. Electric hotplate according to claim 3, characterized in that the cover plate (17) has inwardly directed projections (51), preferably constructed as stamped-out portions, which act on the casing (23) of the thermostat (19), the cover plate (17) and/or the projections (51) being resiliently constructed.

5. Electric hotplate according to one of the preceding claims, characterized in that the open side (7) of the casing body (23) of thermostat (19) faces the hotplate body (1), the projecting insulating parts being formed by rounded and optionally conical projections (8) shaped onto the opening edge (6) of casing body (23).

6. Electric hotplate according to claim 1, characterized in that a cover plate (17a) covering the underside of the electric hotplate (11) leaves free a central zone (14) and in the vicinity of the latter is fitted a separate, perforated cover part (76), which is optionally fixed by means of a centre bolt (16) acting on the electric hotplate (11) in the central zone (14) and which projects through the central portion of cover part (76) and the latter is a perforated sheet metal cup, advantageously the cup-shaped cover part (76) comprising relatively thick, preferably over 0.8 mm thick sheet metal material perforated prior to deformation and whose hole diameter is only a few millimetres, the perforated surface preferably amounting to ¹/₃ to ^z/₃ and in particularly preferred manner over half the total surface and in particular the perforations are provided in the substantially cylindrical casing area of cover part (76) and advantageously the edge of the cover part (76) rests substantially over its entire circumference on a shoulder (80) of the annular cover plate (17b) and presses the same against an edge of the hotplate body surrounding the central zone and preferably the edge of the cover part (76) has an all-round, outwardly directed support flange (79).

7. Electric hotplate according to claim 1, characterized in that the casing body (23) of the thermostat (19b) is open on its side remote from the hotplate body (11) and the switching units inserted in the slot-like insertion openings (27) can be secured against dropping out by means of at least partly covering fixing part (24, 35, 40) insertable in recesses of the casing body and which engages directly on a cover plate (17) covering the bottom of the hotplate body (11) and preferably the fixing part has at least one shoulder (32) for engaging in a hole (26) in the casing body (23) and at least one cylindrical shoulder (33) for engaging in one of the slot-like insertion openings (27) and preferably the fixing part has on its side facing the cover plate (17) at least one stop cam, stop rib or the like (34) and on its side remote from the hotplate body (11) a lug (41) extending through a corresponding opening (42) in the cover plate.

8. Electric hotplate according to one of the claims 3 to 7, characterized in that in the vicinity of the thermostat (19b), cover plate (17) has openings, holes, slots, etc. (43).

9. Thermostat according to one of the preceding claims, characterized in that in the built-in state the snap spring contact (5, 130, 134) and the temperature sensor (4, 127) are located in a horizontal plane.

10. Thermostat according to one of the preceding claims, characterized in that the projecting insulating parts are formed by the end and side walls (6, 115, 117, 119, 121) of the casing body (23, 113) surrounding the open side (7, 124) of the casing area (25, 123) and project preferably by 1 to 3 mm over the snap-action switch (131) and the temperature sensor (4, 127).

11. Thermostat according to one of the claims 2 to 10, characterized in thatthe support (125) carrying the snap spring contact (130, 134) and the bimetallic element (127) is fixed by an automatic locking means acting with a limited longitudinal movement of support (125) with respect to the casing body (113).

12. Thermostat according to claim 11, characterized in that the automatic locking means comprises as the insertion opening (147) at least one depression on the inside of an end wall (115) of casing (113), in which engages one end of support (125) and is also secured therein against movement in the direction of the open side (124) of casing area (123), that in the vicinity of the other end (153) of the support is provided a portion projecting into or through an insertion opening (157) in a further end wall (117), secured in said opening (157) against movement in the direction towards the open side (124), but being received with limited mobility in the transverse direction thereto, as well as being provided with a stop face (159) cooperating with a securing face (161) located on the other end wall (117), the distance between the end of support (125) engaging in the depression and the stop face (159) is greater than the distance between an end wall portion adjacent to the depression and the securing surface (161), but is smaller than the distance from a portion of the associated end wall (117) adjacent to the securing surface (161), and preferably support (125) is pressed by the snap spring contact (130, 134) engaging on the opposite contact (163) in the direction of its position associated with the securing surface (161) and the portion of support (125) projecting through the associated insertion opening (157) forms a connecting tab (153) a lead (155) being insertable between one wall of insertion opening (157) and said portion.

13. Thermostat according to claims 11 or 12, characterized in that the opposite contact (163) cooperating with the snap spring contact (130, 134) is inserted in a preferably cross-sectionally, arcuate or flat V-shaped, slot-like insertion opening (165) and is secured by welding the associated lead (166).

14. Thermostat according to one of the preceding claims, characterized in that both electrical connections (155, 166) of the thermostat (111) are located in the vicinity of the narrow side of casing body (113).

15. Thermostat according to one of the preceding claims, characterized in that the thermostat (19, 19b, 111) constructed for placing in an unheated central zone (14) of the electric hotplate has its open side (124) pointing in the horizontal direction.

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