Electric Relay With a Thermistor Associated With a Casing Enclosing a Thermally Expandable Mass and a Rod Actuating a Rocker Lever

Electric relays, particularly "all-or-none" types, generally comprise an electromagnet actuating an armature with a contact point against a fixed contact to open or close an electric circuit.

Proper operation of the above mentioned types of electric relays require an electromagnet and elastic devices of adequate size so that dependable, rapid opening is assured, and so that the contacts close without bouncing.

One of the purposes of the invention is to reduce the cost of commonly used relays where an electromagnet or solenoid constitutes the most costly component.

Other purposes of the invention are to guarantee rapid, dependable opening of the contacts when the relay goes from the operative to the resting position, and to eliminate contact bounce when the relay closes.

The present relay instead of including an electromagnet to actuate an armature uses an electrothermal device comprising a hermetically sealed casing, enclosing wax or other material with high thermal expandable properties, and an axially mobile rod projecting from said casing, which can come in contact with a rocker lever depending on how far said rod projects from the casing. Said rocker lever, shaped like a quadrant, when pressed by said rod against the reaction of elastic devices, moves horizontally against a cylindrical spring, which in turn causes an armature with a contact point to rapidly move against a fixed contact point closing an electric circuit. Said rocker lever is moved back to the resting position when the thermistor is no longer excited by said springs; a tooth on said rocker lever causes the armature to be retracted away from the fixed contact immediately interrupting the circuit.

The invention will be described further, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a drawing of the relay in the resting position;

FIG. 2 shows the same relay when operative;

FIG. 3 is a vertical cut-away view of the thermoelectric device.

With reference to FIG. 1, the relay housing 1 encloses the rocker lever 3,3a pivoting at 2. One end 3a is anchored with a spring 5, the opposite end 15 having a probe-like configuration is in contact with a cylindrical spring 10. Said spring 10 is anchored at one end on the armature 11a, and at the other end at the internal portion of the edge of the electrical terminal 14.

The armature 11a comprises a contact point 11 and can oscillate with respect to the internal portion of the terminal 14, and is electrically connected with said terminal. Terminal 13 is connected to a contact point 12 facing the mobile contact point 11. Rocker lever 3 comprises a tooth 4 which, when contact points 11 and 12 are closed (FIG. 2), touches the free end of the armature 11a. The head 16a of a rod 16 presses against the arm 3a of a rocker lever 3. Said rod passes through a seal 18 (FIG. 3), and is immersed in a mass 17 that has high thermal expandable properties, which is contained in a hermetically sealed casing 6. A thermistor (PTC) 7 is placed on the outer wall of the thermally conductive casing 6. Electric terminals 8 and 9 are connected to an electrical circuit 19,22 for exciting said thermistor 7. Contacts 11 and 12 are connected to power supply circuit 20,21 intended for any device P requiring power.

Relay operation is as follows:

If circuit 19,22 is supplied with electricity, the PTC 7 heats causing the expansion of the mass 17 and the axial movement of the rod 16 in the direction indicated by arrow --x-- in FIG. 3. The head 16a of rod 16 forces the rocker lever 3 to move counterclockwise in an angular fashion.

The angular motion of the rocker lever 3, one of whose ends 15 is in contact with a spring 10, causes said spring to bend as shown in FIG. 2, creating an imbalance of the armature 11a rapidly forcing it to move from the position shown in FIG. 1 to that illustrated in FIG. 2. This closes contact points 11 and 12 at a high pressure, which is the result of the extreme traction of the spring 10. Under these conditions, contact bounce between contact points 11 and 12 is prevented and the electric power supply circuit 20,21 for any electric device P is closed.

When the thermistor 7 is no longer excited, the temperature of the mass 17 in the casing 6 drops, the reaction of the spring 5 forces the rod 16 back to the position shown in FIG. 1, and brings the rocker lever 3 back to the resting position. The tooth 4 is made of electrically insulated material, and is integral with the rocker lever 3. When said rocker lever 3 moves back to the resting position with an angular, clockwise motion, said tooth 3 touching the free end of the armature 11a rapidly separates contact points 11 and 12, thus preventing sticking of the contacts.

The present relay has a simple structure, is extremely dependable, and is durable considering that the thermally sensitive components 6,7,16 are not subject to failure as solenoids are.

The thermally sensitive component comprising a thermistor 7 can be structured so that the rod 16 moves longitudinally in a different or inverse way with respect to that described. Furthermore, the relay can have multiple contacts instead of the pair 11 and 12.