[0001] The present invention relates to a thermostat comprising a bimetal switch element
reacting upon temperatures, which on one of its ends is fastened on a frame and on
the other end is provided with an electric contact adapted to engage a fixed contact
provided on the frame, said frame comprising two mutually parallel sheet-like metallic
contact carriers forming a base unit, through which two parallel pins are extending
for connection of both contact carriers and on which pins the contact carriers, with
a tight fit, are slidable to and fro one another and permanent mutually parallel during
mounting, which thermostat may be provided with an external heating means, an internal
heating means, a heat capacity, as well as various embodiments of connecting terminals
for the contact carriers.
[0002] Such a thermostat has been described in the not prepublished European patent application
83200914.
[0003] A number of embodiments of said thermostat are shown, influencing the current sensibility
and/or the times of switching it on and off, and/or connection and mounting possibilities.
[0004] For instance various embodiments of connecting terminals for the contact carriers
are shown: an external heating element that is fed by the current to be switched,
possibly arranged in or on a heat capacity; contact carriers, one of which or both
being made in a resistance material, possibly combined with a special configuration
of said carriers and/or an additional heat capacity.
[0005] Furthermore the possibility is indicated of adding to these embodiments a heat source
connected in parallel, preferably with PTC-characteristics, keeping the thermostat
open after being opened until the main current is interrupted, so that a so-called
manual reset function is obtained.
[0006] A drawback of this structure is that an additional component (requiring additional
space) and contact-making means have to be added, whilst special care should be bestowed
on stability, for instance in the event of vibrations. It is a further drawback that
in the automatic reset function, that is without an additional heat source connected
in parallel, the switch-back times highly depend upon the ambient temperature, and
the range of switch-back times is restricted i.e. by the difference between the switch-back
temperature and the ambient temperature.
[0007] While maintaining the advantages with respect to the known thermostats, mentioned
in the above indicated patent application, the invention tends to abolish the above
indicated drawbacks and for that purpose it is characterized in that at least one
of the pins is made of PTC-material, from which pins, when energized, electrically
generated heat can be transferred by conduction, convection and radiation to the temperature
sensitive switching element of the thermostat.
[0008] Because of the application of said feature the possibilities of use are enlarged
by a broader range of switch-back times and reset functions, a simpler mounting without
additional components is possible, minimal room is necessary, said thermostat being
reliable in a fabrication-technical respect and the time at which it switches back
on again can be accurately influenced.
[0009] One, or both, pins can be made of a PTC-material with a predetermined Curie-temperature
with which a simple, solid structure is obtained. Heat generated in this or these
PTC pins is transferred by radiation, conduction and convection to the switching member
of the thermostat. Because of the close construction of the device the Curie-temperature
of the PTC pin, when energized, determines mainly the temperature of the switching
member. At lower ambient temperatures it creates an artificial direct ambient temperature.
When the Curie-temperature of the PTC pin is chosen in such a way that this artificial
direct ambient temperature lies between the switch-off and switch-on temperature of
the thermostat, the latter cannot switch back again when the ambient temperature falls.
Only externally switching-off the current can switch the thermostat on again, a so-called
manual reset function. When the Curie-temperature is chosen in such a way that this
artificial direct ambient temperature in the application at decreased ambient temperatures
in the situation of thermal balance is below and close to the switch-on temperature,
a very long time for switching-on again is provided. This switching-on takes place
automatically and the time of switching-on again depends less upon the ambient temperature.
The closer the Curie-temperature is to the switch-on temperature, the longer the cooling
time of the thermostat will be.
[0010] If one of said pins is made of PTC-material, security is given in case, upon short-circuiting
of the pin, the latterwouldburn. The other pin, made of an insulating material, maintains
the function of the thermostat and the mechanical structure of the whole.
[0011] The invention will be elucidated now on the basis of the drawing.
Fig. 1 shows schematically an embodiment of a thermostat according to the invention.
Fig. 2 shows an upper view of the thermostat of Fig. 1.
[0012] The base unit 1 comprises two mutually parallel, sheet-like contact carriers 2 and
3 which, with a tight fit, are fastened on two parallel pins 4 and 5, one pin or both
pins thereof being made of PTC-material.
[0013] The pins extend through two deep-drawn holes in the contact carriers. The contact
carriers are slidable on the pins to and fro one another and mutually parallel during
the composition and adjustment of the thermostat. Each contact carrier comprises connecting
terminals 6, 6 which are provided on opposite ends of the base unit and are ligned
to one another and extend in longitudinal direction of the base unit.
[0014] One the inner side of one of the contact carriers 2, 3 a switch element 7 is fastened
at 8 on the relevant contact carrier by e.g. welding. The switch element consists
of a bimetal and comprises a setting which enables independent switching with a snap
action at a determined switch-on temperature and switches back at a lower temperature.
[0015] If the direct ambient temperature remains above the switch-back temperature no switching-back
takes place, unless resetting is performed mechanically or the direct ambient temperature
is reduced. The switch-over temperatures are determined by the configuration of the
setting and the manner of mounting.
[0016] The setting is circular in the shown embodiment, however, it may have another shape
too.
[0017] The switch element comprises on its movable end a contact 10 adapted to engage a
fixed contact 11 fastened on the inner side of the other contact carrier. The contact
carriers may have any configuration. For instance they can have an aperture 12 as
illustrated in fig. 1 for laterally exposing almost the entire switch element 7. Furthermore
each contact carrier can be made of a resistance material by which the current sensibility
is increased. The contact carriers can be made of the same material or of two different
materials. A contact can consist of three layers, for instance of Ni, Cu, Ag(Cdo).
It is also possible that the switch element has not been provided with a setting.
The connection terminals can be also have various configurations and positions, and
a heat well can be used as well as the external or an internal heating means.
1. A thermostat comprising a bimetal switch element reacting upon temperatures, which
on one of its ens is fastened on a frame and on the other end is provided with an
electric contact adapted to engage a fixed contact provided on the frame, said frame
comprising two mutually parallel sheet-like contact carriers forming a base unit,
through which two parallel pins are extending for connection of both contact carriers
and on which pins the contact carriers, with a tight fit, are slidable to and fro
one another and permanent mutually parallel during mounting, which thermostat may
be provided with an external heating means, a heat capacity, as well as various embodiments
of connecting terminals for the contact carriers, characterized in that at least one of the pins (4, 5) is made of PTC-material, from which pins, when energized,
electrically generated heat can be transferred by conduction, convection and radiation
to the temperature sensitive switching element of the thermostat.
2. A thermostat according to claim 1,
characterized in that the PTC-material has a Curie-temperature chosen so that the resulting temperature
at the sensing element stays between the switch-off and the switch-on temperature
of the thermostat, when the ambient temperature decreases in the application.
3. A thermostat according to claim 1, characterized in that the PTC-material has a Curie-temperature chosen so that the resulting artificial
direct ambient temperature in the application at decreased ambient temperatures in
the situation of thermal balance is below the switch-on temperature of the thermostat.