Temperature controller having a Bimetallic element and plural heating components

A temperature controller 10 comprises a bimetallic switching device 35 which switches at an excess temperature to protect an electrical device. The bimetallic switching device is accommodated in a housing 12 which has an electrically conductive base and an electrically conductive cover to close this. The cover and the base are connected by an insulation. A first electrical component 17 is connected in series between terminals of the temperature controller at least when the bimetallic switching device is open. A second electrical component 25 being arranged on the bottom of the base is also provided for the bimetallic switching device. The second electrical component 25 is connected in series with the bimetallic switching device 35 between the terminals 37, 39 of the temperature controller 35 at least when the bimetallic switching device 35 is closed. The first electrical component is a he a ting resistor R.sub.H or an insulator 41 with a comparable mechanical construction. The second component 25 is a protective resistor R.sub.V or a short-circuit part 43 with a comparable mechanical construction, so that temperature controllers with purely overheating protection, overheating protection with self-locking function, overheating protection with current sensitivity and overheating protection with self-locking function and current sensitivity can be provided with the same mechanical construction.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a temperature controller with a bimetallic 
switching device which switches at an excess temperature. Such temperature 
controllers are used to protect electrical consumers, for which purpose 
they are connected in series with the consumer so that the consumer's 
operating current flows through the temperature controller. The 
temperature controller is in close thermal contact with the consumer to be 
monitored so that this transfers its temperature to the bimetallic 
switching device. If the temperature of the consumer rises inadmissibly, 
the bimetallic switching device opens and the flow of current to the 
consumer is interrupted. 
2. Related Prior Art 
It is known that this temperature controller can also be provided with a 
self-locking function and/or an excess current sensitivity. 
Such a temperature controller is known from DE-A-41 42 716. 
The known temperature controller comprises a bimetallic switching device 
which opens at an excess temperature or excess current, to which a first 
heating resistor is connected in parallel and with which the second 
heating resistor is connected in series. 
A further temperature controller known from DE-A-43 36 564 comprises a 
ceramic carrier plate with a conductive and insulating coating on which an 
encapsulated bimetallic switching device is arranged, alongside which 
there is a PTC component which is electrically connected in parallel to 
the bimetallic switching device and which acts as a first heating 
resistor. The ceramic carrier plate also bears a thick-film resistor which 
passes below the bimetallic switching device and is connected in series 
with this. The protective resistor does not hereby serve as a protection 
against excess current but to adjust the switching point. 
The object of this known temperature controller is to interrupt the flow of 
current through the electrical consumer if the temperature of this 
consumer rises excessively or possibly also if the current flowing through 
the consumer displays excessive values. For this purpose, the known 
temperature controller is connected in series with the consumer so that 
the current flowing through the consumer also flows through the 
temperature controller, whereby the bimetallic switching device is closed 
at temperatures below the response temperature and/or currents below the 
response current. 
The operating current of the consumer flows with a few ohms through the 
low-ohmic second heating resistor, which is connected in series, and 
through the closed contacts of the bimetallic switching device which 
bridges the first heating resistor. If the temperature of the consumer now 
exceeds a pre-set limit value, the bimetallic switching device, which is 
in thermal contact with the consumer, suddenly opens its contacts in that 
a bimetallic snap disk inside the bimetallic switching devices snaps over. 
The current now flows through the heating resistor connected in series and 
through the second heating resistor, whose resistance is so great that the 
current is much smaller than the original operating current, so that the 
consumer is switched off, in a manner of speaking. As a result of the PTC 
characteristics of the second heating resistor in the temperature 
controller in DE-A-43 36 564, the current drops further when this heating 
resistor heats up. On account of the heat radiation and/or conduction from 
this heating resistor, the bimetallic spring disk is heated up further so 
that it remains self-locked in the position with open contacts. This 
prevents an automatic re-connection of the consumer which has been 
switched off due to an excess temperature following cooling, which could 
lead to a so-called contact flutter with periodic connection and 
disconnection and is usually undesirable. 
If, on the other hand, the current and not the temperature through the 
consumer, and thus the bimetallic switching device, reaches a pre-set 
limit value, the heating resistor connected in series heats up in 
accordance with the description in DE-A-41 42 716 to such an extent that 
the switch mechanism finally reaches its response temperature and opens. 
The self-locking in this case is effected in the same manner as described 
above. 
Although the temperature controller known from DE-A-43 36 564 fulfils a 
number of functional requirements, a disadvantage is that it is relatively 
bulky and large, due in particular to the ceramic carrier plate. For 
reasons of accommodation and thermal capacity, such temperature 
controllers are normally of a very small design, for example they have a 
diameter of 10 mm and a height of 5 mm, which places extreme requirements 
on the manufacturing accuracy and also necessitates a simple yet 
functionally reliable construction. 
Such a miniature design of a temperature controller with self-locking 
through a heating resistor connected in parallel and a heating resistor 
connected in series which is integrated in a very small space for current 
monitoring is known from the generic DE-A-41 42 716. The protective 
resistor is an etched or punched part or a film printed with a resistor 
and is arranged in the direct vicinity of the spring disk of the 
bimetallic switching device, being in thermal and electrical contact with 
this, in such a way that it lies in the bottom half of the housing. 
Apart from the complicated assembly of the known temperature controller, a 
further disadvantage is the fact that the etched or punched part used here 
as a heating resistor is not very accurate with respect to the resistance 
value and can only be made for a small resistance range. Moreover, an 
additional insulating component is also needed between the bottom of the 
housing and the heating resistor, and generally an additional, 
externally-mounted high-impedance resistor in series to the aforementioned 
protective resistor for reasons of resistance adjustment, which on the 
whole increase the costs of construction and overall dimensions. 
Different constructions are known for all of these known temperature 
controllers which do justice to the respective special field of 
application and the special circumstances. However, this leads to the 
necessity of various components for the different temperature controllers, 
so that manufacturers on the whole have to stock large numbers of 
different parts. 
The inventors of the present application have now recognised that this 
problem is due in particular to the fact that new such temperature 
controllers have to be constructed for the different modes of operation of 
the temperature controller. 
SUMMARY OF THE INVENTION 
In view of the above, it is an object of the present invention to provide a 
temperature controller which does not display these disadvantages. 
This object is achieved by the invention by a temperature controller 
designed according to the principle of a modular system with a bimetallic 
switching device which switches at an excess temperature, a first 
electrical component assigned to the bimetallic switching device which is 
connected in series between the terminals of the temperature controller at 
least when the bimetallic switching device is open, and a second 
electrical component assigned to the bimetallic switching device which is 
connected in series with this between the terminals of the temperature 
controller at least when the bimetallic switching device is closed, 
whereby the first component is designed as a heating resistor or an 
insulator with a comparable mechanical construction and/or the second 
component is designed as a protective resistor or a short-circuit part 
with a comparable mechanical construction, so that temperature controllers 
with purely overheating protection, overheating protection with 
self-locking function, overheating protection with current sensitivity and 
overheating protection with self-locking function and current sensitivity 
can be provided with the same mechanical construction. 
The object underlying the invention is thus achieved in full. The inventors 
have recognized, namely, that with a corresponding arrangement of the 
individual parts it is surprisingly possible to design these as either 
resistance elements or as a shortcircuit part/insulator, so that only two 
alternatives of the corresponding components have to be kept in order to 
be able to assemble a total of four different temperature controllers. The 
stocking of various parts as known from the state of the art is thus 
avoided. 
It is then preferred if a housing is provided to accommodate the bimetallic 
switching device which displays a pot-shaped, electrically conductive base 
and an electrically conductive cover to close this, this being connected 
to the base by an insulation, whereby the first component is connected 
between the cover and base, the second component is arranged beneath the 
bimetallic switching device on the bottom of the base, this being 
connected between the base and a contact surface, and the bimetallic 
switching device connects the cover to the contact surface when closed. 
This measure is advantageous from constructional aspects since it creates a 
very compression-proof housing of an electrically conductive base and 
cover which fully encapsulates the bimetallic switching device so that 
this is protected against external influences in a known manner. A further 
advantage is that the new temperature controller can be very easily 
assembled, namely all that has to be inserted into the base in succession 
are the second component, then the bimetallic switching device, then the 
first component and finally the cover, with an interim layer of 
insulation, whereby an electrical connection between the individual parts 
must be ensured during insertion. 
It is then preferred if the second component is a plate covering the bottom 
of the base which is connected between the contact surface and the base, 
whereby the plate either displays an insulating carrier material on which 
a protective resistor is arranged, which is connected to the contact 
surface and the base, or itself represents a short-circuit between the 
contact surface and the base. The contact surface is hereby preferably 
provided on an electrically conductive ring which is arranged between the 
plate and the bimetallic switching device. 
These measures also have advantages for the construction and assembly, 
since either a protective resistor or a short-circuit between the contact 
surface and the base is made by simply inserting the plate into the base 
and laying the electrically conductive ring on this, no other connecting 
measures are required. 
It is then also preferred if the first component is a ring part on which 
the cover rests and through whose ring opening the bimetallic switching 
device makes contact with the cover, whereby the ring part preferably 
rests on an electrically conductive ring disk which makes conductive 
contact with the base. The ring part is hereby either made of a resistor 
material, preferably PTC material, or is an insulator. 
This measure also has advantages for the construction and assembly since 
after insertion of the bimetallic switching device only the electrically 
conductive ring disk and then the ring part itself have to be inserted 
into the base, following which the cover is placed on the ring part. The 
electrical connection between the individual parts results solely through 
the contact and closure of the base with the cover. 
On the whole it is preferred if the bimetallic switching device comprises a 
fixed switching contact borne by the cover and a corresponding movable 
switching contact borne by a spring disk which is moved by a bimetallic 
snap disk and is electrically connected to this, whereby the spring disk 
preferably rests on the contact surface and the movable switching contact 
presses against the fixed switching contact when the bimetallic switching 
device is in its closed state. 
This measure also has advantages for the construction and assembly since 
following insertion of the plate and the electrically conductive ring, the 
spring disk with the movable switching contact which this bears is then 
laid on this ring, the bi-metallic snap disk is then fitted over the 
contact part, after which the electrically conductive ring disk is 
inserted, on which the ring part and then the cover are placed. 
In a further development it is then preferred if a tube-shaped insulating 
part is provided in the base on which the electrically conductive ring 
disk rests. 
The advantage of this is that firstly there is an electrical insulation 
between the base on the one hand and the plate, the spring disk and the 
bimetallic snap disk on the other, whereby this insulation at the same 
time serves as a support for the electrically conductive ring disk via 
which the ring part makes contact with the base. 
Further advantages can be derived from the description and enclosed 
drawing. 
It is understood that the aforementioned features and those to be explained 
in the following can be used not only in the specified combinations but 
also in other combinations or alone without going beyond the scope of the 
present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 shows a new temperature controller 10, comprising a housing 12 which 
displays a base 13 made of electrically conductive material and a cover 
14, similarly made of electrically conductive material, which closes the 
base 13. For this purpose there is an insulating collar 15 between the 
base 13 and the cover 14 which projects beyond the cover 14 on the sides 
and slightly on the top. An edge 16 of the base 13 protrudes beyond this 
insulating collar 15 and is crimped over to close the housing 12. 
The cover 14 hereby rests with its underside on a first electrical 
component 17, which is designed as a ring part 18. The ring part 18 in 
turn rests on an electrically conductive ring disk 19, whose edges make 
conductive contact with the base 13. 
The ring disk 19 has an insulating layer 20 on its underside which points 
away from the ring part 18, via which it rests on a tube-shaped insulating 
part 21. The insulating part 21 has a shoulder 22 which in turn rests on 
an electrically conductive ring 23 on whose upper side there is a contact 
surface 24. 
The ring 23 in turn rests on a second electrical component 25 in the form 
of a plate 26 which is arranged on the bottom 27 of the base 13. The plate 
26 displays a through-connection 28 which makes a conductive contact 
between the base 13 and the upper side 29 of the plate 26. 
A convex spring disk 31, which bears a movable switching contact 32 which 
interacts with a fixed switching contact 33 arranged on the cover 14 
through the ring part 18, rests on the contact surface 24. A bimetallic 
snap disk 34 is fitted over the movable switching contact 32, which in the 
switching state shown in FIG. 1 displays a temperature below its switching 
temperature. 
The spring disk 31, movable switching contact 32, fixed switching contact 
33 and bimetallic snap disk 34 together form a bimetallic switching device 
35, which in the state shown in FIG. 1 makes an electrically conductive 
connection between the cover 14 and the contact surface 24. If the 
temperature of the bimetallic snap disk 24 rises above the switching 
temperature, the bimetallic snap disk suddenly snaps over from a convex to 
a concave shape, after which its outer edge now rests on the insulating 
layer 20 and the movable switching contact is raised from the fixed 
switching contact 33 against the force of the spring disk 31 so that the 
electrical connection between the cover 14 and the contact surface 24 
mentioned above is opened. 
It is mentioned that a litz 38 is provided as a first terminal 37 on the 
cover 14, whereas a further litz 40 is welded onto the edge 16 of the base 
13 as a second terminal 39. 
On account of the chosen construction, the first electrical component 17 is 
connected between the cover 14 and the base 13, whereby a series 
connection of the bimetallic switching device 35 and the second electrical 
component 25 is arranged parallel to this first electrical component, as 
indicated in the electric equivalent circuit diagram shown in FIG. 2. 
The temperature controller 10 described up to now is constructed according 
to the principle of a modular system in that the first electrical 
component 17 and the second electrical component 25 can be designed on the 
one hand as heating resistors, though also as insulators/short-circuit 
parts. The circular part 18 can, for example, be an insulating part 41 or 
a PTC resistor 42. Similarly, the plate 26 can be either an electric 
short-circuit part 43 or a carrier part 44 on which an electrical 
protective resistor Rv is arranged. This protective resistor Rv can, for 
example, run as a thick-film resistor on the upper surface 29 and be 
connected between the electrically conductive ring 23 and the 
through-connection 28. 
Depending on the choice of properties of the components 17, 25 temperature 
controllers 10 with different electrical properties though with identical 
mechanical constructions can thus be manufactured in a modular manner. If, 
for example, component 17 is an insulating part 41 and component 25 a 
short-circuit part 43, the temperature controller 10 assumes a purely 
temperature monitoring function. If component 25 is fitted with a 
protective resistor Rv on the other hand, the temperature controller is 
current sensitive, the flowing current generates heat in the protective 
resistor Rv which ensures that the bimetallic switching device 35 opens if 
the current flow becomes too high. 
If component 17 is designed as a holding resistor R.sub.H the current 
flowing through this component 17 when the bimetallic switching device 35 
is open ensures that sufficient heat is generated keep the bimetallic 
switching device 35 open. When the metallic switching device 35 is closed, 
the resistance of series connection of the bimetallic switching device 35 
component 25 is much lower than the resistance of component so that quasi 
no current flows through this component 17.