Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – With bimetallic elements
Reexamination Certificate
2001-11-30
2003-06-10
Vortman, Anatoly (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
With bimetallic elements
C337S066000, C337S052000, C337S037000, C200S339000
Reexamination Certificate
active
06577221
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a safety switch and, more particularly, to such a safety switch, which uses a S-shaped metal spring plate to guide and support a push and pull bar, enabling the On/Off control bimetal contact plate to automatically trip off upon an overload.
2. Description of the Related Art
FIG. 7
shows a conventional seesaw switch, which comprises a switching handle
11
(which has a lamp bulb installed therein), and a press rod
110
supported on a spring in a bottom hole of the switching handle
11
and moved with the switching handle
11
to move a movable metal contact plate
12
between the “On” position and the “Off” position. This structure of seesaw switch is a passive switch that cannot automatically trip off upon an overload. When an overload occurred, the circuit tends to be burned out. In order to eliminate this problem, switches with protective circuit means, i.e., safety switches are developed.
FIGS. 8A and 8B
show a safety switch according to the prior art. This structure of safety switch comprises a housing
10
, a switching handle
13
pivoted to the housing
10
, three metal contact plates, namely, the first metal contact plate
15
, the second metal contact plate
16
, and the third metal contact plate
17
respectively installed in the bottom side of the housing
10
, a bimetal contact plate
170
, the bimetal contact plate
170
having a fixed end fixedly fastened to the third metal contact plate
17
and a free end provided with a contact
171
adapted for contacting a contact
160
at the second metal contact plate
16
to close the circuit, a link
14
coupled between one end of the switching handle
13
and the free end of the bimetal contact plate
170
and driven by the switching handle
13
, to move the contact
171
of the bimetal contact plate
170
toward or away from the contact
160
of the second metal contact plate
16
, and a curved spring plate
18
fixedly connected between one peripheral sidewall of the housing
10
and the free end of the bimetal contact plate
170
and adapted for controlling the moving distance of the free end of the bimetal contact plate
170
. When the temperature of the bimetal contact plate
170
surpasses a predetermined high value due to an overload, it is caused to deform and to trip off from the contact
160
of the second metal contact plate
16
. This structure of safety switch is still not satisfactory in function because of the following drawbacks:
1. When the switching handle
13
jammed or stopped by an external pressure, or the curved spring plate
18
was worn-out, the bimetal contact plate
170
cannot trip off upon an overload.
2. The bimetal contact plate
170
automatically trips off when the temperature surpassed a trip-off temperature (normally 100°~150° C.). When turning the switching handle
13
to the “On” position at this time, the bimetal contact plate
170
will automatically trip off if the power of deformation of the bimetal contact plate
170
surpasses the spring power of the curved spring plate
18
. If the user holds the switching handle
13
in the “On” position with force to keep the contact
171
of the bimetal contact plate
170
in contact with the contact
160
of the second metal contact plate
16
at this time, the circuit may be caused to burn out.
3. Because the bimetal contact plate
170
is a planar structure for one-way trip-off functioning only, the curved spring plate
18
must be used to achieve bi-directional trip-off functioning. However, it is difficult to control the spring power of the curved spring plate
18
during its fabrication. If the spring power of the curved spring plate
18
does not match, the bimetal contact plate
170
will be unable to function normally.
FIGS. 9A and 9B
show a safety switch with overcurrent protection. This structure of safety switch comprises a switching handle
20
, an electrically insulative driving element
21
and a link
22
coaxially pivoted to one end of the switching handle
20
, a spring member
24
connected between a fixed point and the other end of the driving element
21
, and a bimetal contact plate
23
. The bimetal contact plate
23
has a fixed end fixedly fastened to a first metal contact plate connected to one terminal of power supply, and a free end connected to the other end of the link
22
and moved with the link
22
relative to a contact at a second metal contact plate connected to the other terminal of power supply. When an overcurrent occurred, the bimetal contact plate
23
is heated to deform and to trip off from the contact of the second metal contact plate, and at the same time the driving element
21
is moved upwards with the free end of the bimetal contact plate
23
and forced into engagement with a curved positioning portion
25
in the housing of the safety switch to hold the bimetal contact plate
23
in the “Off” position. This structure of safety switch still has drawbacks. If the switching handle
20
, the driving element
21
, or the link
21
fails to function normally, the bimetal contact plate
23
will be unable to trip off upon an overload. Further, the spring power of the spring member
24
must be accurately controlled during its fabrication. If the spring power of the spring member
24
does not match, the driving element
21
will be unable to function properly.
Therefore, it is desirable to provide a safety switch that eliminates the aforesaid drawbacks.
SUMMARY OF THE INVENTION
The present invention has been accomplished to provide a safety switch, which eliminates the aforesaid drawbacks. It is one object of the present invention to provide a safety switch, which automatically trips off upon an overload. It is another object of the present invention to provide a safety switch, which has a simple structure, and achieves the auto trip-off functioning of a conventional complicated fuseless mechanical switch. It is still another object of the present invention to provide a safety switch, which can be smoothly accurately switched between the “On” position and the “Off” position. To achieve these and other objects of the present invention, the safety switch comprises a housing holding two metal contact plates, which are respectively connected to the two opposite terminals of power supply, a bimetal contact plate suspended from one metal contact plate, a switching handle pivoted to the housing and adapted for moving the bimetal contact plate between the “On” position to close the circuit between the two metal contact plates and the “Off” position to open the circuit between the two metal contact plates, a push and pull bar pivoted to one end of the switching handle and driven by the switching handle to move the bimetal contact plate between the “On” position and the “Off” position, and a S-shaped metal spring plate adapted for supporting and guiding movement of the push and pull bar for enabling the bimetal contact plate to trip off automatically upon an overload despite of the positioning of the push and pull bar or the switching handle.
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Rosenberg , Klein & Lee
Vortman Anatoly
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