[0001] The present invention relates to a thermally actuated switching device, comprising
a base body, an electric switch, a setting spindle, a heat responsive diaphragm, and
means for adjustment the switching threshold temperature, according to the preamble
of claim 1.
[0002] The switching device described in EP-0 377 169 has a setting spindle for adjusting
the desired switching temperature, via the diaphragm which moves an actuating lever
arm further away from or closer to the switching position of the electric contacts,
and a calibration nut, threaded on the spindle and inserted in the base body, the
nut has a circumferential collar, in order to be clamped against the base body, by
means of a clamping bracket which is fastened to the base body by screws. The clamping
force is so strong that the nut rotates with friction with respect to the base body,
when it is turned with the aid of a tool, in order the setting spindle to be axially
displaced during the calibration step, whereas it prevents the nut for being moved
by the normal turning of the setting spindle when the device is in use. During the
calibration step, for advancing the setting spindle, it is gripped in order to prevent
its rotation. The calibration nut according to EP-A-0 377 169 requires a large number
of components and steps to be assembled into the base body.
[0003] In US-3,899,765, the thermally actuated electric switch has a setting spindle or
screw threaded in an insert which is a riveted nut, but it is not a calibration nut
because it does not rotate, it only serves to guide the advance of the screw.
[0004] The object of the present invention is a thermally actuated switching device as is
defined in claim 1.
[0005] In the device according to the present invention, the calibration nut can be held
to the base body in a simple manner by riveting in a bore in the base body. It is
a very reliable and simple technique, allowing a good control of the clamping force
with which the calibration nut clamps in the edge of the bore in a suitable manner,
and there is no need of mounting fits others than the calibration nut itself.
[0006] A washer is interposed between the deformable sections and the base body by suitably
selecting the dimensions and the material of this washer, the clamping force with
which the riveted nut is clamped to the base body can be controlled, to achieve the
reproductivity. In this way, therefore, the amount of force which is required to rotate
the riveted nut during calibration is controlled. Furthermore, the presence of the
washer makes it possible to take up any axial loads which may arise.
- Fig. 1 shows a partial cross-section of the thermally actuated switching device, according
to the invention.
[0007] With reference to the Fig. 1, the device 1 comprises the base body 2 and the actuating
arm 3 provided with a hinge axis 4 and a bent section 5, the diaphragm 6 which is
connected to a hollow sensor 8 via a capillary line 7, and the setting spindle 9 provided
with an intermediate thread 9b interacting with a corresponding thread in the calibration
nut 15 which is mounted on the base body 2. The numeral 10 indicates the switch contacts.
The temperature threshold value at which the switch 10 is opened and closed can be
adjusted with the aid of the setting spindle 9.
[0008] The correct angular position of the setting spindle relative to the temperature indexing,
can be calibrated by placing the sensor 8 in a space with the set known temperature
and then rotating the calibration nut 15 up to meet the switching on-off. During the
rotation of the calibration nut 15, the setting spindle is gripped against rotation,
keeping its flat surface 9a, in the same predetermined angular position as shown in
Fig. 1. After calibration, a drop of sealing wax indicates that calibration has taken
place.
[0009] It is essential that the calibration nut 15, after the calibration step, cannot rotate
during normal use of the device, when the setting spindle 9 is turned to set a temperature
value.
[0010] According to the invention, the calibration nut 15 is riveted in such a way that
it can be rotated only by means of a tool. The riveted nut 15 is arranged in a bore
16 in the base body 2. As a stop, the riveted nut 15 has a shoulder 17 which bears
against the base body 2, and a riveting rim 18 which is riveted to the opposite side
of the base body 2. The washer 20, made of material deformable, is accommodated in
the riveted connection.
[0011] Advantageously, the riveted rim 18 is provided with one slot, in which the special
tool for calibration is engaged.
1. A thermally actuated switching device, comprising a base body (2), an electric switch
(10), a spring-mounted actuating arm (3) for actuating the switch (10), a setting
spindle (9) to set the operating temperature which interacts with the actuating arm
(3), and a calibration nut (15), which interacts with the setting spindle (9), characterized
in that the calibration nut (15) is a riveted nut, and can be rotated with friction
for advancing the setting spindle (9) during the calibration step.
2. The switching device according to claim 1, characterized in that the riveted nut (15)
is accommodated in a bore (16) in the base body (2), and comprises one o more shoulders
(17), which bear against the internal surface of the base body (2), and a deformable
riveting rim (18), which is riveted on the external surface of the base body (2).
