WO2004023507A1

WO2004023507A1 - Sear mechanism

Info

Publication number: WO2004023507A1
Application number: PCT/EP2002/009860
Authority: WO
Inventors: Bernd Siedelhofer; Jörg PUHR-WESTERHEIDE; Simon Powell; Paul Weaver; Jones Agyeman
Original assignee: Abb Patent Gmbh
Priority date: 2002-09-04
Filing date: 2002-09-04
Publication date: 2004-03-18

Abstract

Sear mechanism for mechanically actuating a piece of equipment especially an electric switch or circuit breaker characterized in that it comprises two elements (12, 16) the first (12) of the elements being biased to an actuating condition but held in a non-actuated condition by engagement with the second (16) of the elements.

Description

Sear Mechanism

The present invention relates to a sear mechanism.

Sear mechanisms are known as are their characteristics of producing a quick actuation. We have previously proposed to use sear mechanisms for a number of different purposes usually in conjunction with an electrically operating actuation mechanism. The benefit of this combination is that the sear mechanism produces a quicker output than we would expect from the electrically operating actuation mechanism alone.

Problems remain however. Sear mechanism can be sensitive and thus prone to uncontrolled release when subjected to vibration. Alternatively, when desensitised to overcome this problem they may then lose their speed so that the overall time taken for the combination of sear mechanism and actuation mechanism to operate becomes too long for many purposes.

An object for the present invention is to propose a high speed sear mechanism while be instable and relatively insensitive to vibrations.

The present invention proposes a two- element sear mechanism according to claim 1. The present invention provides a sear mechanism comprising two probably mounted elements, one of the elements being biased to an actuated condition but held in a non- actuated condition by engagement with the other of the elements.

The two elements inter- engage by means of a step and one element co- operating with a shaped portion in the other element. The shape of the shaped portion being such that rotation of the element provided with the shaped portion does not alter the force applied until the amount of rotation causes the shaped portion to leave the step and thus release the element with the step.

In order that the present invention be more readily understood, an embodiment will now be described by means of example with reference to the accompanying which shows an exploded perspective view of an arrangement using a sear mechanism according to the present invention.

The preferred embodiment will be described in relation to actuating an electrical switch or circuit breaker. This is but one use of the mechanism as will be appreciated from the following description even though the description is given in relation to this use.

Turning now to the drawing, a back plate 10 provides a rigid mount on which a sear mechanism 1 is provided. The sear mechanism 10 comprises a first element in the form of a trip bar 12 which is pivotally mounted on the back plate 10 by being located on a pivot shaft 14 provided on the plat 10 the pivot shaft passing through a hole 42 in the bar 12. The mechanism 10 also comprises a second element in the form of a crowbar 16 which is also pivotally mounted on the back plate 10 by being located on a pivot shaft 18 provided on the plate 10.

As will be seen, the pivot point of the trip bar 12 is located nearer one end of the trip bar 12 than the other and this end is provided with an actuation projection 20 for mechanically actuating another piece of equipment, in this case an electrical switch or circuit breaker 21. The projection 20 extends nearly perpendicular to the elongated direction of the trip bar 12. The trip bar 12 is biased to an operating position, in this case biased for counter- clockwise rotation, by means of a bias spring 24 attached to the trip bar 12 near the other end 25 of the bar 12. There the trip bar 12 is provided with a second projection 40 extending parallel to the projection 20 in an opposite direction. With this second projection the bias spring 24 is connected. The other end 25 of the bar 12 is also provided with spaced apart steps 26 and 27 which project out of the plane of the paper and whose purpose will become clear later. Finally, the bar 12 is shaped, in this case provided with a slot 28, to enable the trip bar to rotate without striking the further pivot shaft 18.

The crowbar 16 is located on the pivot shaft 18 passing through a hole 43, and, like the trip bar 12, is pivoted closer to one end 29 than the other 30. The other end 30 is arranged to be acted upon by an actuator which in this case is an electrically operated actuator eg a piezo- electric device. The lines 44, 45 show the shafts 14, 18 passing through the holes 42, 41 , 28, 43. In the present embodiment, the actuator (not shown) engages a ledge 31 on the end 30 of the crowbar 16 and, in use, causes or allows the crowbar to rotate in a clockwise direction.

The end 29 of the crowbar 16 is shaped to form a beak 33 which engages with the step 26 on the trip bar 12. The shape of the beak 33 is such vis- a-vis the step 26 that as the crowbar 16 rotates the force applied to the step 26 will be constant and will counteract the effect of the spring bias until such time as the beak 33 comes off the step 26 suddenly. This sudden action results in the trip bar 12 quickly rotating in a counterclockwise direction under the action of the bias spring 24 and operating the switch or circuit breaker 21.

The actual shape of the beak is not important as long as it provides instantaneous and continued clearance to allow the trip bar 12 to rotate. The end 30 of the crowbar 16 is shaped, in this case slotted with a slot 41 , to prevent the crowbar 16 from striking the pivot shaft 14 as the crowbar 16 rotates. So it is possible to mount the bars 12, 16 in stacked form, and both are arranged parallel to each otherwhere by the shaft or pin 14 passes through the slot 41 and the shaft 18 passing through the slot 28.

In order to reset the sear mechanism 10, all that is required is hat the trip bar 14 is rotated in the anti- clockwise direction eg by pulling on the 20 or by pressing down on the trip bar 14. This rotation causes the step 27 to engage the end 29 of the crowbar and cause the crowbar 16 to rotate in a clockwise direction until the beak 33 again engages the step 26.

The two elements of the sear mechanism 10 can be laminar elements which result in the mechanism being low provide and low mass. Also, the pivot shafts and/or the holes in the devices 12 and 16 can be provided with low friction material in order to ensure that the mechanism operates at high speed. This is further ensured by shaping the trip bar such that is centre of gravity is on the pivot shaft 14 in order to reduce inertia.

The sear mechanism described above thus provides an arrangement which is simple, self-resetting and fast by reducing the forces involved.

Claims

1. Sear mechanism for mechanically actuating a piece of equipment especially an electric switch or circuit breaker characterized in that it comprises two elements (12, 16) the first (12) of the elements being biased to an actuating condition but held in a non- actuated condition by engagement with the second (16) of the elements.

2. Sear mechanism according to claim 1 , characterized in that the two elements (12, 16) inter- engage by means of a step (26) and the first element (12) cooperating with a shaped portion (33) in the second element (16) - the shape of the shaped portion being such that rotation of the second element (16) provided with the shaped portion does not alter the force applied until the amount of rotation causes the shaped portion to leave the step and thus release the first element (12) with the step.

3. Sear mechanism according to claim 1 or 2, characterized in that the first element (12) is mounted rotating around a pivot point (14) which is nearer to the one end which end is provided with an actuation projection (20) for mechanically actuating the piece(21) the Other end being biased into an operating position by a bias spring (24).

4. Sear mechanism according to claim 3, characterized in that the first element is a trip bar(12) which is provided with spaced apart steps (26, 27) which project out of the plan of the tripbar (12) at the second end.

5. Sear mechanism according to one of the claim 1 to 4, characterized in that the second element (16) is shaped as a crowbar which is mounted turnably around a pivot point (18) at the one end which is near the second end of the first element (12) and shaped to form a beak (33) which engages with one (26) of the steps of the first element (12).

6. Sear mechanism according to one of the claims 1 to 5, characterized in that the other end of the second element (16) is provided with a ledge (31) being engaged with an actuator.

7. Sear mechanism according to one of the claims 1 to 6 'characterized in that the elements (12, 16) are mounted to a plate(10) carrying the pivot shafts (14, 18) for turnably mounting of the elements, and that at least the first elements has a slot (28) through which the pivot shaft (18) for the second element (16) passes.