Rapid opening time-delay relay

BACKGROUND OF THE INVENTION

Field of the invention

The present invention relates generally to electrical relays which provide a time-delay after application of power before they close and, more particularly, to delayed-closing relays which open rapidly when power is removed therefrom.

Description of prior art

Prior are time-delay relays generally include a plurality of pairs of electrical contacts carried on thermostatic blades and cooperatively arranged to perform the time delay function upon application of power to the relay. Such relays are unsatisfactory for certain applications because they are slow to open when power is removed therefrom. For example, time delay circuitry has been proposed which includes a relay armature coupled with a movable contact which is alternately engageable with first and second stationary contacts. The first contact is in circuit with a heat motor disposed adjacent thermostatic elements for driving the relay armature, and the second contact is in circuit with the relay coil. When power is applied to the relay, the heat motor is energized to heat the thermostatic elements and move the armature to break the circuit through the heat motor and close the circuit through the relay winding to maintain the relay actuated while the thermostatic elements cool whereby when power to the relay is discontinued the relay will open rapidly. A time delay circuit of this type is shown in U. S. Patent No. 2,484,112. However, time-delay relays of this type have the disadvantage that the thermostatic elements must be relatively large to control the relay armature and consequently are relatively expensive to manufacture.

SUMMARY OF THE INVENTION

The time-delay relay of present invention is characterized by a first electrical contact carried on. the free end of a thermostatic blade and connected in series with the coil of the relay. A second contact is adapted for connection in parallel with a heat motor disposed in heat exchange relationship with the thermostatic blade and is operatively coupled with the armature of the relay for movement into engagement with the second contact when the relay is energized. Application of power to the relay energizes the heat motor to heat and flex the thermostatic blade to engage the first and second contacts thereby causing current in the circuit to bypass the heat motor and energize the relay. While the relay is actuated, the first and second contacts are maintained in engagement irrespective of cooling of the blade. Consequently, when power is lost, the relay will open rapidly regardless of the heated or cooled state of the thermostatic blade.

Other objects and features of the present invention will become apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawing.

DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a time-delay relay embodying the present invention;

FIG. 2 is a top view of the relay shown in FIG. 1;

FIG. 3 is a vertical sectional view taken along the line 3—3 of FIG. 2;

FIG. 4 is an electrical schematic diagram of the timedelay relay shown in FIG. 1; and

FIG. 5 is a front view of the relay shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 3, the time-delay relay of the present invention includes a delay switch, generally designated 10, having a U-shaped bimetallic blade 11 connected in series with a coil 15 and carrying a first electrical contact 17 on its free end. A second electrical contact 21 is carried on the free end of a leaf spring 23 which tends to urge the second contact 21 downwardly into engagement with the first contact 17. The spring 23 is flexed upwardly when the relay is deenergized, by an upstanding piston 25 (FIG. 3) carried from an armature 27 of the relay. A coil of resistance wire 29 is wound on the thermostatic blade 11 to form a heat motor, and is adapted for connection in parallel circuit with the second contact 21. Thus, when power is applied to the relay, the motor 29 heats the thermostatic blade 11, which moves the first contact 17 upwardly into engagement with the second contact 21. This circuit bypasses the motor 29 and energizes the relay coil 15 to pull the armature 27 downwardly to the broken line position shown in FIG. 3. In the energized conditon of the coil 15 the contacts 17 and 21 are maintained in engagement irrespective of cooling of the blade 11. In this regard, cooling of the blade 11 moves the first contact 17 downwardly into a position out of engagement with the second contact 21 when the relay is de-energized and the armature 27 bends the free end of the spring 23 upwardly. This assures rapid opening of the relay without the necessity of waiting for the blade 11 to cool after power to the relay has been discontinued.

The relay of the present invention includes a frame 31 having a base 33 and oppositely disposed, upstanding, side walls 35 and 37. Secured between the upper extremities of the side walls 35 and 37 is a top wall 41 having a plurality of forwardly and rearwardly disposed, coextensive channels 43 therein. As best seen in FIG. 3, a plurality of apertures 45 are formed intermediately in the channels 43 for receiving the respective plungers 25 carried on the armature 27. Referring to FIG. 5, it is noted that the plunger 25 on the right-hand side of the relay is not utilized in the particular embodiment shown.

3,501,718

Forwardly and rearwardly extending contact strips 47 and 49 are supported on the middle two plungers 25 and have their opposite ends disposed over terminals 51 and 53 (FIG. 2), respectively. The terminals 51 and 53 have electrical leads 55 and 57 connected therewith by screws 59 and 61, respectively.

Referring to FIG. 3, the armature 27 includes a top plate 71 on which the plunger 25 is carried and which forms on its opposite ends a pair of downwardly projecting posts 73 and 75 (FIG. 5). A pair of spring rods 77 and 79 are connected between the base 33 and the respective posts 73 and 75 to form spring guides. Compression springs 81 and 83 surround the respective rods 77 and 79 for biasing the armature 27 upwardly to normally maintain the contact strips 47 and 49 spaced above the terminals 51 and 53 and to project the plunger 25 upwardly against the leaf spring 23 to maintain the contacts 17 and 21 spaced apart.

Referring to FIG. 3, the leaf spring 23 is turned under at its left-hand end to form a mounting tab 91 which is secured to the top 41 by a nut and bolt assembly 93.

Referring to FIGS. 4 and 5, the heat motor 29 and leaf spring 23 are connected in parallel and are each connected to one of the power terminals 51 by means of electrical leads 97, 99, and a voltage dividing resistor 101. The thermostatic blade 11 is connected in series with the coil 15, and the opposite end of the coil 15 is connected with a power lead 105.

In operation, when there is no power supplied to the relay of present invention, it will remain open as shown in FIG. 4 with the delay switch 10 open. When power is applied to the relay the current passing through the lead 97, resistor 101, heat motor 29, thermostatic blade 11, and relay 15 is sufficient to heat the thermostatic blade 11. However, the power is insufficient to actuate the relay coil 15. After a predetermined time interval the thermostatic blade 11 becomes heated sufficiently to raise the contact 17 upwardly into engagement with the contact 21 thereby completing the parallel circuit through leads 97, 99, leaf spring 23, thermostatic blade 11, and relay coil 15 to energize such relay and pull the contact strips 49 and 47 downwardly onto the terminals 51 and 53.

Actuation of the relay pulls the plunger 25 downwardly to enable the leaf spring 23 to . assume the broken line position shown in FIG. 3, and thereby maintain the contacts 17 and 21 in engagement after the blade 11 has cooled. Closing of the contacts 17 and 21 also causes current to bypass the resistor 101 and the heat motor 29, allowing the thermostatic blade 11 to cool and assume its relaxed position. Upon deenergization of the relay, the armature 27 is lifted upwardly by the compression springs 81 and 83 to push the left-hand plunger 25 (FIG. 5) upwardly against the leaf spring 23. This raises the second contact 21 out of engagement with the first contact 17 and rapidly breaks the circuit through the coil 15. Thus, when power is again applied, the thermostatic blade 23 is again heated to provide a time-delay before closing of the delay switch 10 and actuation of the relay.

From the foregoing, it will be apparent that the timedelay relay of the present invention provides a convenient and economical means for delaying application of power to an associated electrically operated system, and for rapidly opening the circuit to such system when power has been interrupted. A relay of this type is of particular importance where power is to be rapidly cut off from a device such as a water heater whose limit switch has been opened due to overheating. In cases of this type the relay of the present invention rapidly breaks the circuit to the heating elements to prevent further heating and overpressurization.

Various changes and modifications may be made with regard to the foregoing detailed description without departing from the spirit or the scope of the following claims.