GB2097461A

GB2097461A - Escape door latch

Info

Publication number: GB2097461A
Application number: GB8208130A
Authority: GB
Original assignee: EVERED SECURITY PRODUCTS Ltd
Current assignee: EVERED SECURITY PRODUCTS Ltd
Priority date: 1981-03-19
Filing date: 1982-03-19
Publication date: 1982-11-03
Also published as: GB2097461B

Abstract

An escape door latch includes a bolt (12) which is biased into an extended condition by means of a torsion spring (18) acting differentially on two abutments (25, 26) carried by the bolt. The force which acts on the bolt in the outward direction is applied to the abutment (25) by means of a pivoted member (19), but when a frangible member is broken, the member (19) is caused to move laterally so as to transfer the contact edge (24) from the abutment (25) on the bolt to an adjacent fixed abutment (27) on the casing, with the result that the force applied by the free end of the spring (22) to the other abutment (26) on the bolt is no longer compensated by an opposing, greater force applied to the abutment (25). In this way, the bolt (12) is automatically withdrawn by the torsion spring (15) which normally biases the bolt to its extended condition. <IMAGE>

Description

SPECIFICATION Escape door latch Description of invention This invention relates to escape door latches of a type in which a latch bolt is resiliently biased into an extended position and is normally withdrawn by key-operable driving means, but can be withdrawn in an emergency without the use of a key.

Previously proposed escape door latches of this type have included a breakable member such as a glass panel, breakage of which allows access to an operating lever or the like, which can then be operated to withdraw the latch bolt so that the door can open. It would be desirable to provide for automatic withdrawal of the latch bolt on breaking the breakable member, bearing in mind that a person using the door in an emergency might be in a state of panic, or hindered by smoke or fumes, from following the operating instructions.

However, one of the features of such a door latch is that the latch bolt is resiliently biased into the extended condition, so that the action of closing the door initially displaces the bolt towards its withdrawn condition before the latch bolt engages in a keeper. This has prevented the satisfactory production of an automatically operating escape door latch because this resilient bias has to be overcome, in addition to providing some means, resilient or otherwise, for withdrawing the latch bolt.

It is an object of the invention to provide an escape door latch affording automatic withdrawal of the latch bolt in emergency operation.

According to the invention there is provided an escape door latch comprising a housing; a latch bolt slidably movable relative to the housing between a withdrawn and an extended condition, (the former permitting the door to be opened); key-operated driving means for causing movement of the latch bolt between its extended and withdrawn conditions; resilient biasing means normally acting on the latch bolt to urge it towards its extended condition; and emergency operating means including a frangible member and bias reversing means for at least substantially reversing the directional sense in which the biasing means act on the latch bolt, in response to breakage of the frangible member.

The resilient biasing means may comprise a torsion spring means acting on the latch bolt so as to urge it to the extended condition in normal use of the latch.

The torsion spring means may be centred on a pin on the housing and include two arms acting in opposite directions on respective abutments on the latch bolt, the reaction forces exerted by the abutments on the spring means tending to stress the torsion spring in use.

The relative positions of the pin the arms of the torsion spring means and the abutments are arranged to be such that a greater component of force is exerted in the direction movement of the latch bolt on one abutment than on the other abutment so as to give rise to a nett force in a directional sense such as to urge the latch bolt to the extended condition.

The torsion spring means may comprise a pivoted member, pivotally mounted at said pin on the housing, and a coiled torsion spring mounted concentrically with the pivoted member, one free end of the spring being secured to said pivoted member which acts on one of said abutments, and the other free end of the spring acting on the other of said abutments, the member having a contact edge contacting said one abutment at an angle to the direction in which the latch bolt is movable which is greater than the angle relative to said direction at which said other free end of the spring contacts said other abutment.

The latch bolt will be forced to slide towards the extended condition if the component of the spring force acting to move it in that direction is greater than the component of the spring force tending to move it in the opposite direction. Since the stressed torsion spring exerts an equal force at each of its free ends, the resultant forces on the abutments should be equal. However, by selection of the angle between the direction of application of the force, and the direction in which the latch bolt is constrained to move, the component forces in the latter direction can be arranged to be unequal.

Preferably, the pin is so disposed relative to the abutments that, when the latch bolt is moved away from the extended condition towards the withdrawn condition, for example, during closure of the door, said angle at which the contact edge contacts said one abutment increases more rapidly than the angle at which said other free end of the spring contacts said other abutment so that the nett force acting on the latch bolt increases.

This may be achieved if said one abutment is radially closer to the pin than said other abutment.

The arrangement may be such that the nett force exerted on the latch bolt increases to a maximum at an intermediate position and thereafter decreases, through a neutral condition, to one in which, in the fully withdrawn position, a small nett bias acts in the reverse direction to hold the latch bolt in its withdrawn position when moved to that position by the key-operated driving means.

The bias reversing means may comprise means for automatically disengaging the contact edge of the pivoted member from contact with said one abutment and engaging it with a fixed abutment on the housing.

The pivoted member may be movable laterally clear of said one abutment on the latch bolt by the bias reversing means in a direction along the pivotal axis of the pivoted member.

The bias reversing means may include a spring loaded release member abutting the frangible member and operatively connected to the pivoted member whereby, when the frangible member is broken, the pivoted member is moved in response to the spring loading of the release member in a direction along its pivotal axis.

The release member may comprise a headed plunger having a concentrically disposed coiled spring acting on its head. The pivoted member may be disposed within the housing and secured to the plunger.

The head of the plunger may include a slot or recess to enable it to be rotated by a tool for resetting of the pivoted member after emergency use. The head may be made of, or may include a low friction material normally in contact with the frangible member.

The invention will now be described in more detail by way of example only, with reference to the accompanying drawings, in which Figure 1 is a front elevational view of a latch embodying the invention, with part of the housing removed and certain details including the keyoperable mechanism omitted for clarity; Figure 2 is a similar view of the latch in the withdrawn condition after emergency release; Figure 3 is a sectional view on the line 3-3 of Figure 1; Figure 4 is a sectional view on the line 4-4 of Figure 2.

Referring firstly to Figure 1 of the drawings, a latch generally indicated at 10 comprises a housing 11 which is intended to be inserted in a mortice in a door or secured to the face of the door, and a latch bolt 12 which is slidably mounted in the casing for movement between an extended condition shown in Figure 1 and a withdrawn condition shown in Figure 2. In the extended condition, the latch bolt 12 projects through a forend 13 which is flush with the edge of the door, into a keeper (not shown) provided in the door jamb. The latch bolt is constrained for linear sliding movement by means of a peg 14 engaging in an elongate slot 1 5 in the latch bolt.

The latch bolt may be operated by any suitable means, for example directly by a key acting on the cam surfaces 16, via a key-operated lever mechanism or by a key-operated cylinder. The precise operating mechanism is not relevant to the present invention.

As is customary with latches, the latch bolt is spring biased outwardly to the extended condition shown in Figure 1. However, the latch is fitted with emergency release means generally indicated at 1 7 and illustrated in Figures 3 and 4.

The operation of the emergency release means has the effect of at least substantially reversing the directional sense in which the biasing means acts on the latch bolt, so that the latch bolt is automatically moved into the withdrawn condition shown in Figure 2 by operation of the emergency release means 17.

The biasing force acting on the latch bolt 12 is derived from a coiled torsion spring 1 8 which is mounted with a pivoted member 19 at a fixed point 20 on the housing 11. The pivoted member 19 is of generally U-shape in cross-section as can be seen from Figures 3 and 4 of the drawings. The U-shape member 1 9 has one long limb 1 9a and one short limb 1 9b, and the member is mounted on a pivot pin 23 located at fixed point 20 on the housing 11. One free end 21 of the torsion spring 1 8 passes through an opening in the pivoted member 19 and is effectively rigidly secured thereto. The other free end 22 of the spring 18 extends outwardly away from the pivot pin 23.

The pivoted member 19 has a contact edge 24 which makes contact with a first abutment 25 rigid with the latch bolt 12. A second abutment 26 also rigid with the latch bolt is contacted by the free end 22 of the torsion spring.

The arrangement is such that, when the contact edge 24 is in contact with the first abutment and the free end 22 of the spring is in contact with the second abutment 26, the spring is under torsional compression and thereby the contact edge 24 and free end 22 of the spring act on the abutments 25, 26 in opposite directions.

Since each end of the torsion spring can be expected to give the same resultant force when the spring is stressed, a symmetrical arrangement would not have the effect of moving the latch bolt bodily in either of its possible directions of sliding movement. However, in the arrangement shown, the latch bolt is moved bodily in the direction towards the extended condition shown in Figure 1. This takes place because the angle made by the contact edge 24 with respect to this direction of movement is larger than the angle made by the free end 22 of the spring relative to that direction.

Thus, the component of the force which operates on the latch bolt in the direction of movement on the first abutment is greater than that exerted on the second abutment in the opposite direction.

The torsion spring therefore provides a nett biasing force which moves the latch bolt into the extended position, projecting through the forend 1 3. However, the latch bolt can be withdrawn against the action of the torsion spring by the use of a key in the lock mechanism (not shown).

Such withdrawal of the latch bolt 12 is illustrated in Figure 2 of the drawings, where the fully withdrawn position of the pivoted member 1 9 is shown in chain-dotted lines. As the latch bolt 1 2 is withdrawn, the angle between the contact edge 24 and the direction of movement of the bolt and the angle between the free end 22 of the spring and the direction both increase.

However, because the abutment 25 is radially nearer than the abutment 26 to the pivot pin 23, the first-mentioned angle increases more rapidly, with the result that there is an increase in the nett force acting on the bolt in the direction tending to move it towards its extended position. This is desirable in order to ensure that the bolt is returned to its extended condition after temporary inward displacement by engagement with a keeper during closure of the door.

Preferably, the arrangement as illustrated is such that the abutment 25 moves to a position in which the contact edge 24 extends substantially perpendicular to the direction of movement of the bolt, so that the outward force exerted on the abutment 25 is at a maximum, when the bolt is fully retracted. The nett outward force acting on the bolt thus rises as the bolt is withdrawn. At the same time, the torsion spring 1 8 is stressed further since the free end 22 and the contact edge 24 are brought closer together.

It might be expected that, in such latch arrangement, a further spring would be required to act on the bolt to withdraw it against the normal spring bias, in an emergency. However, the present invention makes use of only the torsion spring 1 8 to force the latch bolt 12 in both directions.

The emergency release means 17 can be of any suitable type which is capable of pulling or pushing the pivoted member 1 9 in the direction of its pivotal axis so that it clears the first abutment 25 and comes into engagement with a fixed abutment 27 positioned on the housing 11 so as to be substantially aligned with the first abutment when the bolt is in its extended position. The free end 22 of the torsion spring is required to remain in contact with the second abutment 26 fixed to the latch bolt and this is ensured by arranging the free end 22 of the torsion spring on the opposite side of the bolt 12 from the long limb 1 9a of the member 19, so that as the limb 1 9a which affords the contact edge 24 is moved onto the adjacent fixed abutment 27, the free end 22 of the spring tends to be moved nearer to the bolt.

The torsion spring now acts between the fixed abutment 27 on the casing through the contact edge 24 and only the second abutment 26 on the bolt latch through the free end 22 of the spring.

The only force acting on the latch bolt is that exerted by the free end 22 of the spring and this drives the abutment 26 in a direction away from the forend 13, thereby pulling the latch bolt into the withdrawn condition as shown in Figure 2, without the use of the key-operated lock mechanism.

The particular form of emergency release means 1 7 illustrated in the drawings includes a spring loaded plunger 28 which is in the form of a headed peg having an enlarged slotted head 29.

The head 29 traps a coiled compression spring 30 against a side wall of the housing 11.

The inner end of the plunger passes through an opening 31 in the wall of the housing. It is externally screw-threaded and is threadedly engaged with an internally screw-threaded boss 32 which is integral with the pivoted member 19.

The pivoted member has a pair of opposed apertures which receive the pivot pin 23 previously referred to. This in turn is journalled for rotation in an aperture 33 in the wall of the housing 11 remote from the plunger 28. The pivot pin 23 is retained by a circlip 34. The aperture 33 is of the same size as the opening 31 for a reason to be explained.

The latch bolt 12 has oppositely extending captive studs which form the first abutment 25 and a similar portion on the other face of the bolt latch. In the normal condition of the latch, the first abutment 25 is almost in alignment with the fixed further abutment 27 on the housing.

The spring loaded plunger 28 is normally compressed by a frangible member such as a glass plate. When the glass plate is broken, the spring 30 moves the plunger 28 outwardly as shown in Figure 4 and the pivoted member 1 9 which is threadedly engaged with the plunger 28 is pulled axially along its pivot pin 23 so that the long limb 1 9a clears the first abutment 25 and comes into engagement with the fixed abutment 27 on the housing. The free end 22 of the spring stiil acting on the second abutment 26, pushes the latch bolt 12 back to the withdrawn condition.

It will be seen that the pivot pin 23 remains in the same position in the housing throughout this operation.

In order to re-set the latch after breakage of the glass, it is only necessary to insert a screwdriver or other tool into the slot 35 of the slotted head, rotate the pivoted member from the full line position shown in Figure 2 to the chain-dotted line position shown in Figure 2 and the spring loaded plunger 28 can then be forced inwardly to return the pivoted member to the condition shown in Figure 3. The pivoted member is then held in as it is allowed return the latch towards tne extended condition. Finally, a fresh sheet of glass or other breakable portion is secured over the head 29 of the plunger as the screwdriver is removed.

It will be appreciated that opening the latch with a key will rotate the pivoted member 1 9 and this will in turn rotate the plunger 28. It is therefore desirable to provide a low friction bearing surface on the head 29 of the plunger so as to reduce the frictional engagement between the head and'the glass or other breakable portion.

In order to permit the latch to be used on righthanded or left-handed doors, all the parts are symmetrical, with the exception of the torsion spring. An oppositely handed latch can be built up by reversing the arrangement of all the parts so that they form a mirror image of the arrangement shown in Figures 3 and 4.

Claims

1. An escape door latch comprising a housing; a latch bolt slidably movable relative to the housing between a withdrawn and an extended condition; key-operated driving means for causing movement of the latch bolt between its extended and withdrawn conditions; resilient biasing means normally acting on the latch bolt to urge it towards its extended condition; and emergency operating means including a frangible member and bias reversing means for at least substantially reversing the directional sense in which the biasing means act on the latch bolt, in response to breakage of the frangible member.

2. An escape door latch according to Claim 1 wherein the resilient biasing means comprises a torsion spring means acting on the latch bolt so as to urge it to the extended condition in normal use of the latch.

3. An escape door latch according to Claim 2 wherein the torsion spring means is centred on a pin on the housing and includes two arms acting in opposite directions on respective abutments on the latch bolt, the reaction forces exerted by the abutments on the spring means tending to stress the torsion spring in use.

4. An escape door latch according to Claim 3 wherein the relative positions of the pin, the arms of the torsion spring means and the abutments are arranged to be such that a greater component of force is exerted in the direction of movement of the latch bolt on one abutment than on the other abutment so as to give rise to a nett force in a directional sense such as to urge the latch bolt to the extended condition.

5. An escape door latch according to Claim 4 wherein the torsion spring means comprise a pivoted member, pivotaliy mounted at said pin on the housing, and a coiled torsion spring mounted concentrically with the pivoted member, one free end of the spring being secured to said pivoted member which acts on one of said abutments, and the other free end of the spring acting on the other of said abutments, the member having a contact edge contacting said one abutment at an angle to the direction in which the latch bolt is movable which is greater than the angle relative to said direction at which said other free end of the spring contacts said other abutment.

6. An escape door latch according to Claim 5 wherein the pin is so disposed relative to the abutments that, when the latch is moved away from the extended condition towards the withdrawn condition, said angle at which the contact edge contacts said one abutment increases more rapidly than the angle at which said other free end of the spring contacts said other abutment

7. An escape door latch according to Claim 6 wherein said one abutment is radially closer to the pin than said other abutment.

8. An escape door latch according to any one of Claims 4 to 7 wherein the bias reversing means comprise means for automatically disengaging the contact edge of the pivoted member for contact with said one abutment and engaging it with a fixed abutment on the housing.

9. An escape door latch according to Claim 8 wherein the pivoted member is movable laterally clear of said one abutment on the latch bolt by the bias reversing means in a direction along the pivotal axis of the pivoted member.

1 0. An escape door latch according to Claim 9 wherein the bias reversing means includes a spring loaded release member abutting the frangible member and operatively connected to the pivoted member whereby, when the frangible member is broken, the pivoted member is moved in response to the spring loading of the release member in a direction along its pivotal axis.

11. An escape door latch according to Claim 10 wherein the release member comprises a headed plunger having a concentrically disposed coiled spring acting on its head.

1 2. An escape door latch according to Claim 11 wherein the head of the plunger includes a slot or recess to enable it to be rotated by a tool to enable the pivoted member to be re-set after emergency use.

1 3. An escape door latch according to Claim 11 or Claim 12 wherein the head of the plunger is made of, or coated with a low friction material normally in contact with the frangible member.

14. An escape door latch substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

1 5. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawings.