Overload relay with means to prevent automatic reset

Abstract

A thermal overload relay is constructed so that it cannot be reset automatically regardless of the position of the reset slide. This is accomplished by loading a reclose spring as the reset slide is being depressed, and then releasing the spring energy suddenly to permit overtravel as the spring returns to its normal energy released position, with this overtravel being sufficient to drive the contact operating toggle mechanism overcenter in the circuit closing direction.

Description

Motor controllers utilizing electromagnetic contactors are usually provided with overload relays for automatically opening the contactor control circuit responsive to over-current conditions. Typically, an overload relay is a heat sensitive device having a spring-powered overcenter toggle contact operating mechanism. In addition, this type of over-load relay includes a manually operable reset slide for closing the overload relay after clearance of over-current conditions. In one mode of operation, the reset slide is maintained in a depressed position so that the overload relay will reset automatically.

However, there are many applications wherein automatic resetting is contrary to intended operation. Under such circumstances it is necessary to provide an overload relay that does not have the capability of resetting automatically even if the reset slide is jammed, taped, or otherwise maintained in its depressed position.

In accordance with the instant invention, automatic resetting of the overload relay is defeated by providing a construction in which a positive manual operation is required for each resetting. As the reset slide is depressed, a reclosing spring is loaded, and the energy stored therein is released abruptly as the reset slide reaches the end of its stroke. Release of this spring energy results in driving a reclose member past its normal position momentarily. In this normal position with the spring energy dissipated, the reclose member is ineffective to close the overload relay. However, overtravel of the reclose member caused by abruptly releasing the stored energy of the spring will close the overload relay.

Accordingly, a primary object of the instant invention is to provide a novel construction for a thermal overload relay.

Another object is to provide an overload relay that is incapable of automatic resetting.

Still another object is to provide an overload relay of this type that requires manual operation of the reset slide for each closing operation.

A further object is to provide an overload relay of this type constructed to utilize the overtravel of a spring-loaded device for impact resetting of the overload relay.

These objects as well as other objects of this invention shall become readily apparent after reading the following description of the accompanying drawings in which:

FIG. 1 is a side elevation of an overload relay constructed in accordance with teachings of the instant invention, with the cover removed to reveal the internal elements.

FIG. 2 is a plan view of the overload relay looking in the direction of arrows 2--2 of FIG. 1.

FIG. 3 is a perspective illustrating the relationship of the resetting elements for the overload relay of FIG. 1.

FIGS. 4a through 4g are diagrams illustrating the positions of the reclose member and movable contact arm for various positions of the reset slide.

FIG. 5 is an exploded perspective illustrating the resetting elements for another embodiment of the instant invention.

FIGS. 6a through 6f are diagrams showing the relationship between the reclose member and movable contact arm of FIG. 5 for different positions of the reset slide.

Now referring to the figures and more particularly to FIGS. 1 through 4g. Thermal overload relay 10 is generally of the type described in U.S. Pat. No. 3,562,688, issued Feb. 9, 1971, to F. W. Kussy et al. for Quick Trip Overload Relay Heaters. More particularly, overload relay 10 includes a molded housing divided along line 11 into base 12 and cover 13 secured together by rivets 14. Disposed externally of housing 12, 13 at the edge of opening 15 are spaced apart main circuit terminals 17, 18, each of which is generally L-shaped. U-shaped heater unit 99 is disposed within main cavity 16 and is provided with out-turned legs 97, 98 having clearance apertures which receive screws 19 that removably secure heater 99 to terminals 17, 18. Auxiliary wire grip 96 is mounted to an extension of terminal 17.

Also disposed within cavity 16 is main tripping bimetal 20 which is a striplike member having its upper end 21 welded to the offset upper end of formed stiff support strip 22. Bimetal 20 is interposed between heater 99 and support 22, with the main central portion of support 22 extending generally parallel to heater leg 94. The central portion of support 22 is provided with a threaded aperture that receives the threaded portion of adjusting screw 23 having a large stud 24 disposed externally of base 12 at one end thereof. Rotation of adjusting screw 23 is effective to pivot the lower end of support 22 about abutment 26, above adjusting screw 23, as a pivot. Leaf spring 27 biases support 22 clockwise about pivot 26 and in so doing biases adjusting screw head 24 to the left against base 12. Thus, as screw 23 is turned to pivot support 22 counterclockwise with respect to FIG. 1, the upper end 21 of bimetal 20 will pivot counterclockwise about abutment 26 as a center, thereby moving lower end 31 of main bimetal 20 to the right with respect to FIG. 1.

Reversely bent auxiliary bimetal 35 is secured by rivets 34 to the lower end 31 of main bimetal 20. Free end 36 of auxiliary bimetal 35 is operatively engaged with the right end 42 of translator bar 41 extending through a notch therein. Bar 41 also includes a clearance notch for stationary contact member 45 and main operating spring 46. The latter is operatively engaged by left end 43 of bar 41 as the latter is moved to the right with respect to FIG. 1 by the combined deflections of bimetals 20, 35 as a result of heat generated by current flowing in heater 99.

One end of stationary contact member 45 extends externally of housing 12, 13 at the bottom thereof to constitute plug-in stab 47, and the other end of member 45 is reversely bent and mounts stationary contact 51. The latter is engageable by movable contact 52 mounted at the upper end of movable contact arm 50. The lower end of contact arm 50 is bifurcated and is seated in notches 53 in upper surface of bifurcated extension 54 of conducting element 55. Lower end 48 of element 55 extends externally of base 12 through the lower end thereof and constitutes a plug-in stab.

Main operating spring 46 is a coiled tension member secured at its upper end to contact arm 50 just below movable contact 52. The lower end of spring 46 is secured to extension 56 of member 55, positioned below the lower end of contact arm 50. It should be obvious to those skilled in the art that main operating spring 46 and movable contact arm 50 are connected and operatively positioned to form a spring powered overcenter toggle mechanism for opening and closing cooperating contacts 51, 52 with a snap action. Opening is accomplished automatically upon predetermined movement of bar 41 to the right with respect to FIG. 1. Protrusion 59 extending inward from cover 13 provides a stop which establishes the open circuit position of contact arm 50. Manually depressible reset slide 60 is biased upward by wire spring 61 so as to project above the upper end of housing 12, 13 and, as will hereinafter be seen, is utilized to reclose contacts 51, 52.

Secured to reset slide 60 and extedning downward from the lower end thereof is reclose member 62 constructed of spring material. As slide 60 is manually depressed, the lower end 63 of reclose member 62 engages and then rides along the inclined upper surface 64 of stationary deflector 65, thereby deflecting the lower end of reclose member 62 to the right with respect to FIG. 1. This deflection continues and becomes more pronounced as the deflection of member 62 increases. At a predetermined point in the downward reset stroke of member 60, the lower end 63 of member 62 moves below cam surface 64 and deflector 65 is aligned with clearance notch 66 in member 62. This permits release of the stored spring energy in member 62 causing lower end 63 thereof to snap to the left with respect to FIG. 1 and in so doing end 63 engages movable contact arm extension 67 to pivot the latter counterclockwise with respect to FIG. 1.

Because of the energy stored in reclose member 62, there is a considerable overtravel for end 63. That is, end 63 moves to the left of its normal or rest position illustrated in FIG. 4a and in so doing drives movable contact arm 50 to the left of its so-called neutral position wherein spring 46 is centered so that it does not urge contact arm 50 to move toward either open or closed positions. When reclose member 62 comes to rest with slide 60 held partway along its return stroke, the former abuts the left end of deflector 65. Even in this position of reclose member 62 movable contact arm 50 is free to be on the open circuit side of the neutral position for the toggle which operates movable contact arm 50.

FIGS. 4a through 4g illustrate the deflection of reclose member 62 for progressive positions of reset slide 60 as it is being depressed and released from its depressed position. Thus, it is seen that even if reset slide 60 is maintained in its fully depressed position of FIG. 4d, upon automatic opening of contacts 51, 52, the lower end 63 of reclose member 62 will not move contact arm 50 to the circuit closing side of the toggle neutral position. Because of this a discrete operation of reset slide 60 through its closing stroke is required in order to close contacts 51, 52.

In the embodiment of FIGS. 5 and 6a through 6g, arm 150, mounting movable contact 152 at its upper end, is pivoted at its bifurcated lower end portions 153, 153 and is operated into circuit opening and closing positions by an overcenter toggle mechanism including main operating spring 146. By depressing reset slide 160 the lower cam surface 161 of deflector 162, at the lower end of reset slide 160, engages inclined surface 163 at the right end of reclose member 164 moving the latter to the left. When this occurs, coiled compression spring 165 is loaded and this loading continues until the upper end of cam surface 161 passes below reclose member 164 at which time the energy stored in spring 165 is suddenly released driving member 164 to the right with respect to FIG. 5. Because of kinetic energy positioning spring 166 is partly compressed and spring 165 expands beyond its normal at-rest position. This permits reclose member 164 to drive contact arm 150 to the right of the neutral position of the toggle mechanism so that spring 146 is then effective to bring movable contact 152 into engagement with stationary contact 172.

Thus, it is seen that the instant invention provides constructions for thermal overload relays which prevent automatic resetting regardless of the position of the reset slide.

Although in the foregoing preferred embodiments have been discussed, many variations and modifications will now become apparent to those skilled in the art, and it is therefore understood that this invention is not limited by the disclosure but only by the appending claims.

Claims

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. An overload relay including a stationary contact, a movable contact mounted for movement between a first position engaged with said stationary contact and a second position separated from said stationary contact, a repositionable overcenter spring means connected to said movable contact to bias the latter to said first position when said movable contact is on one side of a neutral position and to bias said movable contact to said second position when said movable contact is on the other side of said neutral position, over-current responsive means operative upon the occurrence of predetermined overload conditions to automatically operate said movable contact to said second position, a manual operating member operable in a reset stroke to reset said movable contact to said first position, a reclose member, biasing means normally maintaining said reclose member in a rest position on said other side of said neutral position, deflector means operatively positioned to engage said reclose member as said operating member is operated to move in said reset stroke, with engagement of said deflector means and said reclose member moving the latter and thereby loading said biasing means, said deflector means and said operating means being constructed so that operative engagement thereof is broken abruptly when said operating member reaches a predetermined point in said reset stroke whereby energy stored in said biasing means is released moving said reclose member into engagement with said movable contact to drive the latter to said one side of said neutral position from which point said spring means closes said contacts.

2. An overload relay as set forth in claim 1 in which the deflector means is stationary, said biasing means is mounted to said operating member, and said reclose member is mounted to said operating member.

3. An overload relay as set forth in claim 2 in which the biasing means and the reclose member are portions of a common member.

4. An overload relay as set forth in claim 3 in which the common member extends from one end of the operating member and generally in the direction of movement for the operating member in its said reset stroke.

5. An overload relay as set forth in claim 4 in which the common member is elongated and is constructed of spring sheet stock, said deflector means including a cam surface that engages the reclose member and deflects the latter away from the neutral position on the other side thereof.

6. An overload relay as set forth in claim 5 in which the operating member is biased in a first direction and movement thereof in said reset stroke is in a direction opposite to the first direction.

7. An overload relay as set forth in claim 1 in which the deflector means is mounted to the handle and movable therewith.

8. An overload relay as set forth in claim 7 also including means mounting the reclose member for movement generally at right angles to movement of the operating member.

9. An overload relay as set forth in claim 8 in which the deflector means and the reclose member include cam formations that engage during movement of the operating member in the reset stroke to move the reclose member away from the neutral position on the other side thereof.

10. An overload relay as set forth in claim 9 in which the operating member is biased in a first direction and movement thereof in said reset stroke is in a direction opposite to the first direction.