NZ757267A - Magnetic door latch and lock mechanism - Google Patents

Abstract

A latch for a hinged or pivoting door has a latching mechanism supported by a housing, the latching mechanism including a magnetically operable latch bolt for reciprocating movement between an extended position and a retracted position. First and second actuators are disposed to opposite sides of the door, each of the first and second actuators being coupled to the latching mechanism to effect withdrawal of the latch bolt from its extended position to its retracted position upon operation by a user. First and second locking devices are disposed to opposite sides of the door, each of the first and second locking devices being coupled to the latching mechanism to lock the bolt in its extended position upon operation by the user. e door, each of the first and second actuators being coupled to the latching mechanism to effect withdrawal of the latch bolt from its extended position to its retracted position upon operation by a user. First and second locking devices are disposed to opposite sides of the door, each of the first and second locking devices being coupled to the latching mechanism to lock the bolt in its extended position upon operation by the user.

Description

– 1 – Magnetic Door Latch and Lock Mechanism Field of the invention The present invention relates to door latch and lock mechanisms having a magnetically operated bolt action. Embodiments of the invention may utilise keyed bolt actuation and locking in conjunction with push-pull user actuators.

Background A door latch assembly conventionally includes a spring-biased latch head that projects from the edge of a hinge-mounted door which is arranged to engage a strike plate in a corresponding door frame. The latch head is typically disengaged (retracted) by means of the user turning or twisting a door knob or handle to actuate the latch mechanism and manually retract the latch head, allowing the door to open. A characteristic of spring-biased moving latches is that the latch head is always resiliently biased to its extended position whether the door is open or closed.

In some applications it is desirable for a door to be opened by pushing or pulling on a handle, rather than by turning or twisting. For example, push/pull door latches have been found particularly suitable for use on doors to hospital rooms and the like, wherein the door typically opens into the room. A hospital door provided with a push/pull type latch may be opened from the outside by applying pressure to the push side of the latch, and opened from the inside by pulling on the pull side of the latch. A push/pull operated latch allows for a hospital technician to enter a patient's room while carrying an armload of medical equipment by merely applying pressure to the push side of the latch, thereby unlatching the door and pushing it open. Conversely, a patient who may have limited use of his or her arms because of the presence of a cast or the like, can unlatch a door and open it from the inside by pulling on the inside handle, an effort requiring a minimum of dexterity.

In a magnetically operated door latch, the latch head remains retracted while the door is open and the latch head is drawn out into its extended configuration by magnetic forces when it aligns with the strike plate aperture in the door frame. This operating – 2 – principle avoids certain difficulties that may be associated with an ordinary spring-biased latch, and also has other benefits, such as:  improved safety and aesthetics since the latch bolt remains retracted while the door is open and the strike plate does not require a protruding lip;  relatively quiet operation since the latch head is not required to impact the strike plate;  the door latch may be equally used on doors that open in either direction, or on doors that swing in both directions.

Notwithstanding the potential benefits of magnetically operated door latches and, in given circumstances, push/pull latch actuators, there are challenges involved in integrating them together in a manner that enables the benefits to be realised while also including a full range of features, such as operation in both a 'passage mode' and a 'privacy mode'. There are further challenges involved in applying the principles of a magnetic door latch and/or a push/pull user actuation system to a lockable door latch assembly (e.g. deadbolt lock), as may be necessary for an external door for example.

Summary of the invention In accordance with one aspect of the present invention there is provided a latch for a hinged or pivoting door, comprising: a housing adapted for mounting in or on a door; a latching mechanism supported by the housing, the latching mechanism including a latch bolt supported for reciprocating movement between an extended positon and a retracted position, the latch bolt including a bolt head having a magnetic component wherein the latch bolt is operatively drawn to its extended position by magnetic force when the bolt head in use aligns with a magnetically susceptible strike member mounted on a corresponding door fixture; first and second actuators disposed to opposite sides of the door, each of the first and second actuators being coupled to the latching mechanism to effect withdrawal of the latch bolt from its extended position to its retracted position upon operation by a user; and first and second locking devices disposed to opposite sides of the door, each of the first and second locking devices being coupled to the latching mechanism to lock the bolt in its extended position upon operation by a user. – 3 – The latching mechanism may include a latch slider assembly supported by the housing for reciprocating movement between a forward position and a rearward position, wherein the latch slider assembly is coupled to the latch bolt such that the rearward position of the latch slider assembly corresponds to the retracted position of the latch bolt, and the forward position of the latch slider assembly corresponds to the extended position of the latch bolt, and wherein the first and second actuators and the first and second locking devices are coupled to act upon the latch slider assembly.

The latch bolt may be coupled to the latch slider assembly by means of a rack and pinion mechanism. The rack and pinion mechanism may include a pinion gear carried by the latch slider assembly that is arranged to mesh with a first rack gear carried by the latch bolt. The rack and pinion mechanism may further include a second rack gear fixed in relation to the housing and arranged to mesh with the opposite side of the pinion gear from the first rack gear.

The rack and pinion engagement between the latch slider assembly and latch bolt effects a displacement doubling whereby the displacement between the extended and retracted positions of the latch bolt is substantially double the displacement between the forward and rearward positions of the latch slider assembly.

In embodiments, the first and second actuators may each comprise a push/pull action user-operable actuator.

Each push/pull action user-operable actuator may comprise: a mounting member adapted for mounting on the door in relation to the latching mechanism; a handle member pivotally supported by the mounting member for movement between a resting position and an operative position; and a lever arm coupled to the handle member and extending into the housing for operative engagement with the latching mechanism, wherein pivotal movement of the handle member from the resting position to the operative position effects swinging motion of the lever arm operative to effect withdrawal of the latch bolt, in use.

The handle member may be pivotally supported by the mounting member for pivotal movement about a vertical axis. – 4 – In embodiments the handle member includes a handle pull portion or a handle push portion or both a handle pull portion and a handle push portion, and wherein the handle member is user-operable for movement between the resting position and the operative position by pulling and/or pushing on the handle member as appropriate relative to the face of the door.

The push/pull door latch actuator may include a spring arranged to apply a bias force to urge the handle member into the resting position in the absence of user action.

Each push/pull actuator lever arm may be arranged to act upon the latch slider assembly whereby user operation of the push/pull actuator from the resting position to the operative position effects displacement of the latch slider assembly from its forward position to its rearward position.

The latch slider assembly may include a bolt carriage and a carriage shuttle that is mounted for movement with the bolt carriage but arranged to permit relative displacement against a spring bias, and wherein the first push/pull actuator lever arm is arranged to act upon a surface of the bolt carriage and the second push/pull actuator lever arm is arranged to act upon a surface of the carriage shuttle.

The latch may further include an entry lock mode mechanism having a privacy engagement member moveable between a first position and a second position, wherein the privacy engagement member when in the second position engages with the carriage shuttle to prevent displacement of the latch slider assembly by the second push/pull actuator.

The entry lock mode selection mechanism may include a user operable privacy pin coupled to the privacy engagement member to enable movement of the privacy engagement member between the first and second positions.

The first and second locking devices may each include a respective key-operated lock cylinder. The first and second lock cylinders are preferably arranged to opposite – 5 – sides of the latching mechanism with respect to the direction of movement of the latch bolt.

The first and second lock cylinders may be coupled to engage with the latch slider assembly of the latching mechanism by way of respective rack and pinion mechanisms.

The latch slider assembly may include a gear shuttle having first and second rack gear formations disposed to opposite sides thereof. The first and second lock cylinders are fitted with respective concentric shuttle pinion gears arranged to engage with the respective first and second rack gear formations of the gear shuttle.

In embodiments the latch slider assembly includes at least one ball bearing carried by the gear shuttle and arranged to lock the latch slider assembly in its forward position by displacement of the gear shuttle by means of user rotation of one of the first and second lock cylinders.

In accordance with another aspect the present invention provides a latch for a hinged or pivoting door, comprising: a housing adapted for mounting in or on a door; a latching mechanism supported by the housing, the latching mechanism including: a latch bolt supported for reciprocating movement between an extended position and a retracted position, the latch bolt including a bolt head having a magnetic component wherein the latch bolt is operatively drawn to its extended position by magnetic force when the bolt head in use aligns with a magnetically susceptible strike member mounted on a corresponding door fixture, and a latch slider assembly supported by the housing for reciprocating movement between a forward position and a rearward position, and wherein the latch slider assembly is coupled to the latch bolt by way of a rack and pinion mechanism; first and second actuators disposed to opposite sides of the door, each of the first and second actuators being coupled to the latching mechanism to effect withdrawal of the latch bolt from its extended position to its retracted position upon operation by a user; and – 6 – first and second locking devices disposed to opposite sides of the door, each of the first and second locking devices being coupled to the latching mechanism to lock the bolt in its extended position upon operation by a user.

In accordance with another aspect of the present invention there is provided a latch mechanism for a hinged or pivoting door, comprising: a housing adapted for mounting in or on a door; a latch slider supported by the housing for reciprocating movement between an extended position and a retracted position; at least one user operable actuator capable of driving the latch slider from the extended position to the retracted position; a latch bolt supported by the housing for reciprocating movement between an extended position and a retracted position and coupled to the latch slider by means of a rack and pinion gear mechanism, the latch bolt including a bolt head having a magnetic component; wherein the latch bolt is operatively drawn to its extended position by magnetic force when the bolt head in use aligns with a magnetically susceptible strike member mounted on a corresponding door fixture.

Further aspects, features and advantages of the present invention will be apparent to those of ordinary skill in the art from the accompanying description and drawings.

Brief description of the drawings In order that the invention may be more easily understood, the following detailed description is provided including description of several embodiments, presented by way of example only, and with reference to the accompanying drawings in which: Figure 1 is an exploded perspective view of components of a magnetic door latch and lock set according to an embodiment of the invention having pull-operated door handle actuators; Figure 2 shows the latch and lock mechanism components from of Figure 1; Figure 3 shows the door handle and actuator components from Figure 1; Figure 4A is an overhead perspective view of the assembled latch and lock set seen in central horizontal section, illustrating the latch bolt in a retracted configuration; – 7 – Figure 4B shows the lock and latch set of Figure 4A in central vertical section; Figure 5A is an overhead perspective view of the assembled latch and lock set seen in central horizontal section, illustrating the latch bolt in an extended configuration; Figure 5B shows the lock and latch set of Figure 5A in central vertical section; Figures 6A and 6B are overhead perspective views of the latch and lock set seen in central horizontal section, illustrating retraction of the latch bolt by operation of the inside and outside handles, respectively; Figures 7A-7C are overhead perspective views of the latch and lock set seen in central horizontal section, illustrating engagement of the privacy lock mechanism; Figure 7D shows an enlarged section of Figure 7C; Figures 8A and 8B are overhead perspective views of the latch and lock set seen in central horizontal section, illustrating disengagement of the privacy mechanism by operation of the inside handle; Figure 9 shows the lock and latch set in central vertical section with the bolt retracted; Figure 10 is a central vertical section of the latch and lock set with the bolt extended into the strike; Figures 11A and 11B show the lock and latch set in central vertical section illustrating engagement of the deadbolt locking mechanism by means of the inside and outside keys, respectively; Figure 12 shows a portion of the lock and latch set in central vertical section illustrating a tactile feedback mechanism; Figure 13 shows a portion of the latch and lock set in central horizontal section and seen from overhead perspective view illustrating locking via a ball locking mechanism; Figures 14A-14C show a portion of the latch and lock set in central horizontal section and seen from overhead perspective view illustrating detail of the ball locking mechanism; Figures 15A-15C show the lock and latch set in central vertical section illustrating the operation of unlocking and unlatching the bolt by means of the inside or outside key; Figure 16 shows the lock and latch set in central vertical section illustrating a double action rack and pinion arrangement for extended bolt throw; and – 8 – Figures 17 and 18 are front and rear perspective views, respectively, of one handle assembly illustrating the use of an installation alignment key; Figures 19 and 20 are front perspective views of a handle assembly having provision for storage of the installation alignment keys.

Detailed description Conventionally, a deadbolt is a mechanism for securing a door in a closed condition. It is referred to as 'dead' because there are no springs (or equivalent) to operate the bolt, as there may be in a door latch mechanism. Rather, it is only operated manually with a key or, in some configurations, with a turn-snib on one side of the door. A mechanism that requires use of a key from both sides of the door is often called a double- cylinder deadbolt lock, whereas a mechanism with a turn-snib on one side is called a single-cylinder deadbolt lock.

A magnetic door latch does not necessarily require a spring-loaded latch head since magnetic forces used to extend the latch head only apply when the door is closed.

Thus, a magnetic latch head in some respects resembles the head of a deadbolt mechanism. Embodiments of the present invention illustrated in the accompanying drawings and described hereinbelow exploit this characteristic and provide a feature-rich magnetic door latch and lock set capable of several distinct modes of operation, such as:  a passage mode  an entry lock mode  a security lock mode.

The resulting magnetic latch and lock set can thus be used in a wide variety of applications, including external doors where security against unwanted entry to a room or building is of concern.

The passage mode, as conventionally understood, allows the door to which the latch and lock set is fitted to be opened from either side by way of user operable actuators (e.g. door handles or the like). In the described embodiment the user operable actuators are in the form of push/pull handles. – 9 – The entry lock mode permits the latch and lock set to be configured so that the door can only be opened by way of the user operable actuator from one side (e.g. the 'inside'). This is akin to a conventional 'privacy mode' although with a small but important difference. Conventionally a latch with a privacy mode has provision for the privacy mode to be disengaged from the 'outside' by inserting a pin or tool into a small aperture provided in the outside faceplate. However, this is undesirable for an external/entry door where unauthorised access is of concern. Accordingly, the entry lock mode as the term is used herein refers to the ability of the latch to be configured for free operation from the inside but only by way of a key from the outside. Nevertheless the term 'privacy' may be used herein when referring to the function of the entry lock mode for convenience of nomenclature, bearing in mind the function may not be identical with conventional understanding.

The security lock mode corresponds to the function of a deadbolt, wherein operation of the latch to open the door is only possible using a key, from both the inside and the outside. Moreover, a key is required to engage the security lock mode, at least from the outside. For safety considerations it is possible to provide a turn-snib in place of a key-operated lock on the inside of the door.

On a note of terminology, features of the door latch assembly, mechanisms and components may be described herein using reference to relative orientations or directions such as left/right, upper/lower, forward/back, and the like. In general such terms are to be understood as referring to the assembled latch mechanism as if it were installed in a door, where the direction in which the latch head extends is considered the 'forward' direction.

Thus, considering the latch head extension direction as forward, the door has left and right faces.

In the description that follows, with regard to door structures in which the door latch may be installed, reference may also be made to the 'inside', 'inner' or 'internal' and 'outside', 'outer' or 'external' which are commonly used terms that delineate features that lie to one side or the other of the doorway. It should be appreciated these terms are generally used in a relative sense that does not necessarily imply or import other meanings or features unless clearly stated. Moreover, when considering the door having – 10 – a forward direction as defined by the latch head extension, the left-hand side may be the 'inside' and the right-hand side may be the 'outside', or vice versa.

Certain features of the door latch mechanism are similar on both sides of the door when installed, while other features may be different for the inside and outside. For example, in the case of a door latch with a privacy mode mechanism each side of the door may have similar user-operated handle actuators but different access to and engagement with the privacy setting mechanism. For ease of reference, similar features of the embodiments that are provided on each side of the door are designated by a reference numeral followed by a suffix 'A' or 'B' corresponding to respective sides of the door. It will be appreciated that A or B may arbitrarily correspond to left or right, inside or outside, unless otherwise stated.

Push/pull handle actuators herein generally refer to latch actuator handles that are operable by the user through pushing and/or pulling in order to operate the latch and open the door. This is in contrast to conventional door latch actuators wherein a twisting or turning action of the handle door handle or knob is required to operate the latch, followed by a push or pull to open the door. Some of the door latch actuators described herein permit only one of a push or pull action to operate the latch, while others allow the user a choice of a push or pull action.

An exemplary embodiment of a lock and latch set employing a magnetic latching action and having low-profile user-operable locks and push/pull handles is shown in various views in the accompanying drawings, with functions and features thereof described hereinbelow. Figure 1 shows the primary functional components in an exploded perspective view, collectively indicated by reference numeral 100. For ease of reference the magnetic door lock and latch set (typically in its assembled condition, as described below) may be simply referred to herein as "the latch 100".

It is convenient to consider the magnetic door lock and latch set 100 in terms of several interacting sub-assemblies as indicated generally in Figure 1. A latch and locking mechanism 10 includes most of the primary functional components and, when installed, at least substantially resides within the structure of a door (not seen). A corresponding strike – 11 – is in use installed in a corresponding door frame or the like, in alignment with the latch and locking mechanism 10. On each side of the door there is provided a handle assembly that allows the user to operate the functions of the latch 100. Specifically, inner and outer handle assemblies 110A, 110B are provided, which are generally similar in structure apart from some differences predominantly related to assembly of the latch 100, explained below.

The main components of the latch and locking mechanism 10 and strike 20 are shown in exploded perspective view in Figure 2 and labelled with individual reference numerals. Similarly the components of the inner and outer handle assemblies 110A, 110B are shown individually labelled in Figure 3. A list of components and corresponding reference numerals is provided at the end of the description.

The general structure of the latch and locking mechanism 10 comprises an elongate housing having lower and upper casing components 30, 35 which, when assembled together, support therein a bolt 40, bolt carriage 50 and gear shuttle 60, along with associated parts as described hereinbelow. The lower casing 30 has a faceplate 31 at its forward end that lies flush with the swinging edge of a door when installed, in conventional manner. Thus, when installed the rest of the housing and components therein lie at least substantially within the door structure, apart from a head portion 42 of the bolt 40 which selectively protrudes through an aperture in the faceplate 31, as explained below.

The strike 20 is in use installed in a door frame or similar structure, aligned with the latch and locking mechanism 10 in conventional manner. The strike 20 has a strike plate 22 surrounding a strike cavity 24. A strike magnet 26 is provided at the end of the strike cavity 26. The bolt head 42 also contains a magnet 41, wherein the magnetic polarities of the bolt head magnet and strike magnet are arranged to attract one another.

As explained further hereinbelow, when the bolt head in use aligns with the strike cavity magnetic forces draw the bolt head magnet toward the strike magnet whereby the bolt is drawn from a retracted position to an engaged position. In the engaged position the head portion 42 of the bolt 40 extends forward of the faceplate 31 and into the strike cavity 26. – 12 – When the bolt 42 head is engaged in the strike cavity the door in which the latch 100 is installed is held (closed) relative to the corresponding door frame or structure.

The inner and outer handle assemblies 110A, 110B may be adapted for push and/or pull operation by the user, although the handles illustrated are for pull-only. In general terms each handle assembly 110 comprises a faceplate 112 that is operatively mounted to the door and secured in relation to the latch and locking mechanism 10. A handle 114 is supported by the faceplate 112 for pivotal movement about a vertically oriented handle pin 116, and biased to a resting position by action of a handle spring 118.

An actuator arm 120 projects inwardly (i.e. into the door) from the handle 112. Each actuator arm 120 comprises an actuator head 121 and an actuator spacer 122, and the extent to which the arm 120 projects is adjustable by use of an actuator spacer 122 of selected length. The faceplates 112A, 112B are operatively fastened to one another by means of faceplate fasteners 113 (e.g. bolts) and each faceplate 112 is, in use, concealed by a respective cover plate 124 attached by way of magnets (not seen in the drawings).

Handle assemblies having this general structure and their use to operate a magnetic door latch is described in detail in the specification of Australian patent application AU2018903406, the entire contents of which are hereby incorporated by reference.

Before proceeding to describe the various operations of the latch 100 in detail it is convenient to first outline the primary functions, as follows: i) Latch The latching function relates to the ability of the bolt to automatically engage with the strike when the door is closed. In the embodiments described herein the latching function relies on magnetic attraction between the bolt and the strike. ii) Unlatch Unlatching relates to the ability of the user to effect retraction of the bolt in order to open the door. Unlatching is typically accomplished through manipulation of the inner or outer handle, but can also be achieved by use of a key in one of the inner or outer lock cylinders. iii) Entry Lock – 13 – The entry (privacy) lock is a function that is engageable from one side of the door only (i.e. the inside of the door). The privacy lock disables the ability of the outside handle to perform the unlatching operation. The privacy lock can be disengaged by several methods from the inside of the door, or by use of a key in the outside lock cylinder. iv) Deadbolt Lock Engagement and disengagement of the deadbolt lock function is accomplished by use of a key in one of the inside or outside lock cylinders. When the deadbolt lock function is engaged neither of the inside and outside handles are able to effect retraction of the bolt.

Latching Figures 4 and 5 illustrate the latch 100 assembled as if installed in a door (although the door itself is not shown) with the bolt in retracted and extended configurations, respectively. In order to observe interior componentry Figures 4A and 5A show the latch 100 in central horizontal section, and in Figures 4B and 5B a central vertical section view is presented. Notably, in Figure 4 where the bolt is retracted the end of the bolt head 41 lies flush with the front surface of the faceplate 31. The configuration of the latch 100 as seen in Figure 4 corresponds to the condition of the latch when the door is open. Conversely, in Figure 5 where the bolt is extended the bolt head 42 projects forward of the faceplate 31 and into the strike cavity 24. The configuration of the latch 100 as seen in Figure 5 corresponds to the condition of the latch when the door is closed.

The transition of the latch from the Figure 4 to the Figure 5 configuration corresponds to the aforementioned latching function that takes place when the door in which the latch is installed is closed. Upon closing the door the faceplate 31 aligns with the strike plate 22 such that the end of the bolt head 42 is lined up with the strike cavity 24. When so aligned, forces of magnetic attraction between the strike magnet 26 and the bolt magnet 41 draw the bolt head forward and into the strike cavity 24. This is permitted by the bolt 40 being slidably supported within the casing (between the lower casing 30 and upper casing 35). The extent of forward displacement of the bolt is limited by a flange on the rear of the bolt and a corresponding shoulder formation on the inside of the lower and/or upper casing. – 14 – In the assembled lock and latching mechanism 10 there are several components arranged within the casing to cooperate with one another as the bolt extends, and to allow retraction of the bolt by user action. This includes the bolt carriage 50 which is slidably supported in the casing and located behind the bolt 40. The forward end of the bolt carriage 50 carries a pinion gear 45 mounted on pinion pin 46 for rotation about a horizontal axis transverse to the direction of the bolt movement. The pinion gear meshes on one side with the teeth of casing rack 32 provided on the inside of the lower casing 30.

The other side of the pinion gear 45 meshes with the teeth of bolt rack 44 provided on the inside of the bolt 40. This arrangement is best seen in Figures 4B and 5B. When the bolt 40 is drawn forward by magnetic force the engagement between the pinion gear 45 and the bolt racks 44 causes the pinion gear to rotate (in a clockwise direction as seen in the Figures). Since the pinion gear is also engaged with the casing rack 32, rotation of the pinion gear causes the pinion gear to move in the forward direction, drawing the bolt carriage 50 along with it.

As a result of the rack and pinion arrangement with the bolt carriage being coupled to the pinion gear, the amount of forward displacement of the bolt carriage 50 is one-half of the forward displacement of the bolt itself. Conversely, rearward displacement of the bolt carriage 50 can effect twice the amount of rearward displacement of the bolt 40.

Location of the bolt head in the strike cavity prevents the door in which the latch is installed from being opened. Once the bolt is extended or 'thrown' the bolt head remains held in the strike cavity by the magnetic attraction forces until being withdrawn by action of a user in one of several ways as explained below.

Unlatching Figures 6A and 6B are perspective views of the latch 100 seen in central horizontal section and illustrating the unlatching function by means of the inside and outside handles, respectively.

In the assembled latch 100 the inside and outside handle assemblies 110A, 110B are mounted to the door (not shown) at opposite sides of the latch and locking mechanism 10. The casing has corresponding slot-like apertures on each side that allow – 15 – the ends of the respective actuator arms 120A, 120B to reach into the casing for interaction with the bolt carriage 50. In Figure 5A the latch 100 is seen in the latched configuration with each of the handles in their resting condition, wherein the actuator arms 120A, 120B project into the casing from each side. A surface of the bolt carriage 50 rests against the rear of the inside actuator arm 120A, held in that position by the magnetic force acting on the bolt magnet. Similarly, in the latched configuration a surface of the tab shuttle 55 rests against the rear of the outside actuator handle 120B, biased into that position by shuttle spring 56 acting between the bolt carriage and the tab shuttle.

Figure 6A shows the latch 100 with operation of the inside handle assembly 110A effecting the unlatching function. In the handle assembly 110A the handle 114A is mounted to the faceplate 112A for pivotal movement about vertically oriented handle pin 116A, with the actuator arm 120A being located to the opposite side of the pivot axis from a portion of the handle adapted for the user to grasp and pull. As a result of this arrangement, when the user pulls on the handle causing it pivot about the pin 116A, the end of the actuator arm 120A pivots in a rearward direction, as can be seen by comparison of Figures 5A and 6A. In this rearward movement the end of the actuator arm 120A bears against a surface of the bolt carriage 60, forcing the bolt carriage to move in a rearward direction within the casing. As described above, the rack and pinion gear coupling between the bolt carriage 50 and the bolt 40 means that rearward movement of the bolt carriage results in double the amount of rearward movement of the bolt which is sufficient to fully withdraw the bolt head from the strike cavity.

But for the entry lock (privacy) function of the latch 100 (explained in detail below) the operation of the outside handle assembly 110B to effect the unlatching function could be implemented in the same way as the inside handle. However, in the embodiment as shown the outside actuator arm 120B bears against a surface of the tab shuttle 55 instead of the bolt carriage itself. The tab shuttle 55 is arranged with a degree of forward-rearward movement relative to the bolt carriage 50 for the purposes of the privacy lock operation.

Nevertheless, when the outside handle is pulled by the user as seen in Figure 6B, pivotal movement of the handle 114B causes the end of the outside actuator arm 120B move in the rearward direction while bearing against the surface of the tab shuttle 55. The tab – 16 – shuttle 55 in turn bears against the bolt carriage 50 causing the bolt carriage to move in the rearward direction and retract the bolt 40 as previously described.

Once the bolt has been retracted by the user pulling on one of the inside and outside handles the door in which the latch is installed can be opened by pulling or pushing on the door. If the handle is released before the door is opened the bolt will extend back into the strike cavity and return to the latched state.

Although the embodiment shown in the drawings and described in detail herein has door handles that operate by the user pulling on a portion of the handle, it will be readily apparent from the disclosure provided in the aforementioned Australian patent application AU2018903406 that other forms of handles can alternatively be employed, including handles that operate by a pushing action instead of a pulling action.

The unlatching function can also be accomplished through operation of either the inside or outside lock assemblies 80A, 80B, the details of which are explained in connection with the deadbolt locking functions hereinbelow.

Privacy locking The privacy locking function allows a user from the inside of the door to activate the privacy lock, without use of a key, and thereby prevent the door being unlatched by means of the outside handle. The privacy locking function can be deactivated by use of the inside handle, or by use of a key in either of the inside or outside lock cylinders.

The enabling mechanism for the privacy locking function includes a privacy push pin 90 that extends through the inside faceplate 112A and cover plate 124A. One end of the privacy push pin 90 is accessible to the user on the inside of the door, and the other end is connected with the privacy pin inner 92 located within the casing of the latch and locking mechanism 10. The privacy push pin 90 and privacy pin inner 92 are supported by the casing for displaceable movement transverse to the direction of movement of the bolt and bolt carriage. In the description of the latching and unlatching functions provided hereinabove, the privacy push pin 90 and privacy pin inner 92 have remained in their – 17 – inactive position (e.g. as seen in Figures 4 and 5), and the privacy pin inner is biased toward the inactive position by means of the privacy spring 94.

Figure 7A shows the latch 100 in the latched state wherein the bolt head is extended into the strike cavity, with the privacy function inactive. This allows latching and unlatching as described above. From this configuration the privacy function is engaged by the user pushing on the privacy push pin 90 as indicated by arrow 'P' in Figure 7B.

The privacy pin inner 92 has a rearwardly extending privacy engagement projection 95 that is hook shaped with a sloped end face. The sloped end face of the projection 95 is aligned with a complementary sloped face provided on a privacy formation 52 of the bolt carriage 50. As the privacy pin is pressed inwardly (Figure 7B) the sloped end face of the projection 95 engages with the sloped face on the carriage privacy formation 52 causing the bolt carriage 50 to marginally displace in the rearward direction against the magnetic force on the bolt, allowing the privacy engagement projection 95 to pass over.

As the privacy push pin 90 is pressed further (against the bias force of spring 94) the privacy engagement projection 95 goes past the carriage privacy formation 52 whereupon the bolt carriage 50 is able to return to its full latched position as shown in Figure 7C. At this point the carriage privacy formation 52 overlaps with the privacy engagement projection 95, preventing the privacy push pin and privacy pin inner from returning to their inactive position. Moreover, the hook portion of the privacy engagement projection 95 is engaged with a shuttle privacy formation 57 which restrains movement of the tab shuttle 55.

When the privacy lock is engaged as shown in Figures 7C and 7D, the tab shuttle is unable to move in the rearward direction by virtue of the shuttle privacy formation being engaged by the hooked end of the privacy engagement projection 95. As a result, the outside handle is unable to perform the unlatching function.

Ordinarily, deactivation of the entry (privacy) lock may be accomplished by the user pulling on the inside handle 114A. The corresponding actions are illustrated in – 18 – Figures 8A and 8B. Figure 8A illustrates the latch 100 with privacy lock engaged immediately upon the inside handle 114A being operated by the user. As shown, pulling on the handle 114A causes the actuator arm 120A to press rearwardly on the bolt carriage 50. While the tab shuttle 55 is restrained by the engagement between the projection 95 and the formation 57 the bolt carriage 50, as previously noted, has a degree of free movement relative to the tab shuttle. This allows the bolt carriage to displace backward until the carriage privacy formation 52 is clear of the privacy engagement projection 95 (Figure 8A). Once the carriage privacy formation 52 is clear of the privacy engagement projection 95 the privacy pin inner 92 and privacy push pin 90 are able to return to their inactive position under bias force from the privacy spring 94, wherein the shuttle privacy formation 57 is no longer restrained by the privacy engagement projection 95 (Figure 8B). From this condition either of the inside and outside handles can operate to perform the unlatching function as previously described.

The privacy lock can also be released from the inside or outside by use of a key in the inside or outside lock cylinder, as will be explained following description of the lock assemblies and their operation in the latch and lock assembly 100.

Deadbolt lock The magnetic door latch and lock assembly 100 includes inside and outside lock cylinder assemblies 80A, 80B which, in conventional manner, are rotatable by means of a corresponding key. The axes of the lock cylinders are orthogonal to the movement axis of the bolt, and the lock cylinder assemblies 80A, 80B are disposed below and above the bolt axis, respectively. Each of the lock cylinder assemblies is fitted with a shuttle gear 82A, 82B in the form of a concentric sleeve. Each shuttle gear 82A, 82B has several radially projecting gear teeth 83A, 83B formed on the exterior thereof, and has at least one lock cylinder engagement lug 84A, 84B formed on the interior. The shuttle gears are able to rotate freely relative to their respective lock cylinders except where the engagement lug encounters a corresponding lock cylinder lobe 81. The shuttle gear teeth are adapted to mesh with transverse grooves formed in the top and bottom of the gear shuttle 60, forming upper and lower rack and pinion gear mechanisms. Apertures are provided in the lower and upper casings 30, 35 to permit engagement between the respective shuttle gears 82 and the shuttle racks 62. – 19 – The general structure and operation of a low profile double-cylinder deadbolt lock mechanism employing the configuration of upper and lower rack and pinion gears is described in detail in the specification of international patent publication WO2018/217477, the entire contents of which are incorporated by reference herein.

Figure 9 shows a side sectional view of the latch 100 with the bolt retracted, and Figure 10 shows a similar view of the latch with the bolt extended. The shuttle 60 is coupled with the bolt carriage 50 with a degree of relative movement permitted by engagement of the shuttle pin 65 in a carriage shuttle slot 51. When the bolt is thrown the shuttle travels forward with the bolt carriage by force on the shuttle pin 65 applied by the rear of the carriage shuttle slot 51. Both shuttle gears rotate in correspondence with the gear shuttle 60 when the bolt is thrown. They are able to move independently of the respective lock cylinders due to the circumferential free travel between the lugs 84 and lobes 81. In other words, when the bolt is thrown by magnetic attraction (e.g. transition from Figure 9 to Figure 10) the shuttle 60 travels forward accordingly and the shuttle gears 82 freewheel independently of the lock cylinders.

Engaging the deadbolt locking function is accomplished by keyed operation of either one of the inside or outside lock cylinders, as illustrated in Figures 11A and 11B.

Specifically, Figures 11A and 11B show engagement of the deadbolt locking function by way of the inside and outside lock cylinders, respectively. For reference, comparison may be made with Figure 10 which shows a similar view of the latch 100 without the deadbolt lock engaged.

With reference to Figure 11A, engagement of the deadbolt locking function using the inside lock cylinder requires the user to insert the corresponding key in the inside lock cylinder (80A) and rotate the lock cylinder in the clockwise direction (as seen in the drawing; anticlockwise from the point of view of the user). Through this action the inside lock cylinder rotates until the cylinder lobe 81A encounters the engagement lug 84A.

Further rotation of the lock cylinder then causes the shuttle gear 82A to also rotate by force of the cylinder lobe 81A on the engagement lug 84A. Rotation of the inside shuttle gear 82A drives the gear shuttle 60 forward by engagement of the shuttle gear teeth 83A – 20 – with the lower shuttle rack 62A. Movement of the gear shuttle 60 with respect to the bolt carriage 50 is restricted by the shuttle pin 65 located within the carriage shuttle slot 51.

Figure 11A shows the furthest forward displacement of the gear shuttle 60 relative to the bolt carriage 50, where the shuttle pin 65 reaches the forward edge of the slot 51 (c.f.

Figure 10 where the shuttle pins is located at the rear of the slot 51).

Figure 11B shows the equivalent action using the outside lock cylinder (80B) to drive the gear shuttle 60 forward by way of the outside shuttle gear 82B. Similarly, the user rotates the outside lock cylinder using the corresponding key, turning in an anticlockwise direction (the same as viewed in the drawing).

Although the location of the shuttle pin 65 in the slot 51 restricts the limit of rotation of the inside/outside lock cylinders, an additional tactile feedback device may also be included to provide the user with a positive indication that the deadbolt lock has been engaged. The tactile feedback device can be seen best in the enlarged view of the gear shuttle 60 shown in Figure 12. Specifically, the gear shuttle 60 carries a spring loaded detent pin 63 that is arranged opposite the shuttle pin 65, separated therefrom by a portion of the bolt carriage that comprises the floor of the carriage shuttle slot 51. The detent pin 63 is urged toward the surface of the bolt carriage by a spring 64. Moreover, the surface of the bolt carriage is formed with a small depression 53 located in the position corresponding to the location of the detent pin 63 when the gear shuttle is in the deadbolt-locked condition as seen in Figure 12. The end of the spring loaded detent pin 63 entering and leaving the depression 53 during the deadbolt locking and unlocking operations provides the user with the aforementioned tactile feedback. The spring loaded detent pin 63 also serves to increase friction between the gear shuttle and bolt carriage to stop unintentional rearward travel of the gear shuttle, for example by vibration or the like.

The effect of driving the gear shuttle 60 to its forward position using the inside or outside lock cylinder to thereby engage the deadbolt lock function is explained hereinbelow with reference to Figures 13 and 14. In particular, Figures 14A-C illustrate the sequence of latch component interactions resulting in engagement of the deadbolt lock function. – 21 – Figure 14A shows detail of the latch 100, seen in horizontal section, wherein the bolt is extended but the deadbolt lock is disengaged (e.g. similar to the condition of the latch 100 as shown in Figure 10). On each side, generally adjacent the location of the detent pin 63, sits a ball bearing 68 within a gap between the rear of the bolt carriage 50 and the inside surface of the lower casing 30. Shown in Figure 14B, as the gear shuttle 60 is advanced relative to the bolt carriage 50, respective ramped surfaces 67 formed on the gear shuttle 60 are arranged to force the ball bearings 68 outwardly and into respective recesses 38 formed in the lower casing 30. By the time the gear shuttle 60 has reached its fully advanced position (as seen in Figure 14C) the ball bearings 68 are trapped in the respective recesses 38 by flat surfaces adjacent the bearing ramps 67 of the gear shuttle 60. This is the deadbolt locked configuration of the latch 100, which is also shown in Figure 13.

When the latch 100 is in the deadbolt locked configuration (Figure 13, 14C) the bolt carriage 50 is prevented from rearward movement (retraction) by the ball bearings 68.

More particularly, the bolt carriage 50 is unable to retract due to the ball bearings 68 being trapped between the rear of the bolt carriage and respective lip formations 37 defining the bearing recesses 38. This configuration prevents any retraction of the bolt carriage 50 (and thus of the bolt 40), including by means of either the inside or outside handle.

Disengagement of the deadbolt lock requires the gear shuttle 60 to first be retracted (relative to the bolt carriage 50) which can only be accomplished by keyed operation of either the inside or outside lock cylinder. The deadbolt lock disengagement and retraction sequence is illustrated in Figures 15A-C and described below in the context of the operation by way of the outside lock cylinder.

The latch 100 as seen in Figure 15A (in vertical section) is in the deadbolt locked configuration as described above. The bolt head 42 is extended and engaged within the strike cavity 24, and the gear shuttle 60 is fully advanced with respect to the bolt carriage 50 wherein the shuttle pin 65 is located at the forward extent of the slot 51. Keyed rotation of the outside lock cylinder (80B) in the clockwise direction, as seen in Figure 15B, effects engagement of the respective lock cylinder lobe 81B with the shuttle gear engagement lug 84B causing rotation of the shuttle gear 82B and resulting in retraction of the gear – 22 – shuttle 60 to the point where the shuttle pin 65 is at the rearward extent of the slot 51.

This action corresponds to the reverse sequence of Figures 14A-C, resulting in release of the ball bearings 68 that prevent rearward movement of the bolt carriage when the deadbolt lock is engaged. Further keyed rotation of the lock cylinder and corresponding rearward movement of the gear shuttle 60 is accompanied by withdrawal of the bolt by virtue of the shuttle pin 65 acting on the rear of the carriage shuttle slot 51. The result is shown in Figure 15C.

Keyed operation of the outside lock cylinder turning the shuttle gear 82B to retract the gear shuttle 60 and in turn the bolt carriage 50 also effects disengagement of the privacy lock should it be in use. The inside key can perform the same function, however disengaging privacy by operating the inside handle, as previously described, is generally easier.

For a secure deadbolt latch it is highly desirable that the bolt is significantly engaged within the strike – in other words the bolt should have a substantial throw length.

However, to maintain a compact design of the latch as described herein presents limitations on the amount of travel that is possible to generate by operation of the push/pull handle actuators and keyed lock cylinders. The rack and pinion gear mechanism employed in coupling the bolt 40 to the bolt carriage 50 provides the solution to this issue by enabling the bolt throw to be double the amount of travel of the bolt carriage. This is illustrated by Figure 16 which shows the latch 100 in vertical section with bolt extended (top) and bolt retracted (bottom). As shown, the amount of travel of the bolt carriage is indicated by 'T' whereas the corresponding length provided to the bolt throw is twice that amount. For example, if the push/pull handle actuators are only able to impart 10mm of travel to the bolt carriage, the amplification effect of the rack and pinion mechanism still enables the bolt head to extend by 20mm.

Figures 17-20 illustrate a handle assembly according to an embodiment of the invention including an installation alignment key 130 that may be used during installation of the latch and locking mechanism in a door. In order for the latch and lock mechanism to function as intended following installation, it is important that the inner and outer handle assembly components be properly aligned with the corresponding latch mechanism – 23 – components. Specifically, because the shuttle gear 82 has an amount of rotational free- play with respect to the lock barrel 80, it is importation that these two components be in a known predetermined alignment with one another during installation so that the shuttle gear functionally meshes in correct alignment with the teeth of the shuttle rack 62.

Accordingly, for the purposes of the installation procedure, an installation alignment ‘key’ 130 is provided, which can be inserted into the key slot of the lock cylinder 80. A corresponding slot is provided in the shuttle gear 82 (see Figure 18) so that when the alignment key 130 is in place the lock cylinder and shuttle gear have a predetermined alignment with one another. Two alignment keys 130 may be provided, one for each of the inside and outside handle assemblies. The alignment keys 130 can be stowed for later use, in a receptacle 131 formed in the faceplate 112 of the inside handle assembly (Figures 19 and 20). As previously noted, once installed the faceplate is covered with a magnetically secured cover plate 124.

The invention has been described by way of non-limiting example only and many modifications and variations may be made thereto without departing from the spirit and scope of the invention. It may also be noted that while operational and functional components of the embodiments have been described and illustrated, various fasteners that may be used to secure the components together and to the door and door frame structure have been omitted in the interest of simplicity.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. – 24 – Compendium of Reference Numerals 100 magnetic door latch and lock assembly ("the latch") latch and locking mechanism strike 22 strike plate 24 strike cavity 26 strike magnet lower casing 31 faceplate 32 casing rack upper casing 37 lip formations 38 bearing recesses 39 case sheath 40 bolt 41 bolt magnet 42 bolt head 44 bolt rack 45 pinion gear 46 pinion pin 50 bolt carriage 51 carriage shuttle slot 52 carriage privacy formation 53 detent depression 55 tab shuttle 56 shuttle spring 57 shuttle privacy formation 60 gear shuttle 62 shuttle rack 63 detent pin 64 detent bias spring 65 shuttle pin 67 bearing ramps – 25 – 68 ball bearings 80A, 80B inside, outside lock assembly 81A, 81B inside, outside lock cylinder lobes 82A, 82B inside, outside shuttle gear 83A, 83B inside, outside shuttle gear teeth 84A, 84B inside, outside lock cylinder engagement lugs 90 privacy push pin 92 privacy pin inner 94 privacy spring 95 privacy engagement projection 110A, 110B inside, outside handle assemblies 112A, 112B inside, outside faceplate 113 faceplate fasteners 114A, 114B inside, outside handle 116A, 116B inside, outside handle pin 118A, 118B inside, outside handle spring 120A, 120B inside, outside actuator arm 121A, 121B inside, outside actuator head 122A, 122B inside, outside actuator spacer 124A, 124B inside, outside cover plate 130 installation alignment key 131 installation alignment key storage receptacle – 26 –

Claims (23)

CLAIMS 1.:

1. A latch for a hinged or pivoting door, comprising: a housing adapted for mounting in or on a door; 5 a latching mechanism supported by the housing, the latching mechanism including a latch bolt for reciprocating movement between an extended position and a retracted position, the latch bolt including a bolt head having a magnetic component wherein the latch bolt is operatively drawn to its extended position by magnetic force when the bolt head in use aligns with a magnetically susceptible strike member mounted on a 10 corresponding door fixture; first and second actuators disposed to opposite sides of the door, each of the first and second actuators being coupled to the latching mechanism to effect withdrawal of the latch bolt from its extended position to its retracted position upon operation by a user; and first and second locking devices disposed to opposite sides of the door, each of 15 the first and second locking devices being coupled to the latching mechanism to lock the bolt in its extended position upon operation by a user.

2. A latch according to claim 1 wherein the latching mechanism includes a latch slider assembly supported by the housing for reciprocating movement between a forward 20 position and a rearward position, and wherein the latch slider assembly is coupled to the latch bolt such that the rearward position of the latch slider corresponds to the retracted position of the latch bolt, and the forward position of the latch slider assembly corresponds to the extended position of the latch bolt, and wherein the first and second actuators and the first and second locking devices are coupled to act upon the latch slider 25 assembly.

3. A latch according to claim 2 wherein the latch bolt is coupled to the latch slider by means of a rack and pinion mechanism. 30

4. A latch according to claim 3 wherein the rack and pinion mechanism includes a pinion gear carried by the latch slider that is arranged to mesh with a first rack gear carried by the latch bolt. – 27 –

5. A latch according to claim 4 wherein the rack and pinion mechanism further includes a second rack gear fixed in relation to the housing and arranged to mesh with the opposite side of the pinion gear from the first rack gear. 5

6. A latch according to claim 5 wherein the rack and pinion mechanism effects a displacement doubling whereby the displacement between the extended and retracted positions of the latch bolt is substantially double the displacement between the forward and rearward positions of the latch slider. 10

7. A latch according to any preceding claim wherein the first and second actuators each comprise a push/pull action user-operable actuator.

8. A latch according to claim 7 wherein each push/pull action user-operable actuator comprises: 15 a mounting member adapted for mounting on the door in relation to the latching mechanism; a handle member pivotally supported by the mounting member for movement between a resting position and an operative position; a lever arm coupled to the handle member and extending into the housing for 20 operative engagement with the latching mechanism, wherein pivotal movement of the handle member from the resting position to the operative position effects swinging motion of the lever arm operative to effect withdrawal of the latch bolt, in use.

9. A latch according to claim 8 wherein the handle member is pivotally supported by 25 the mounting member for pivotal movement about a vertical axis.

10. A latch according to claim 8 or 9 wherein the handle member includes a handle pull portion or a handle push portion or both a handle pull portion and a handle push portion, and wherein the handle member is user-operable for movement between the 30 resting position and the operative position by pulling and/or pushing on the handle member as appropriate relative to the face of the door. – 28 –

11. A latch according to any one of claims 8 to 10 wherein the push/pull door latch actuator includes a spring arranged to apply a bias force to urge the handle member into the resting position in the absence of user action. 5

12. A latch according to any one of claims 8 to 11 as appended directly or indirectly to claim 2 wherein each push/pull actuator lever arm is arranged to act upon the latch slider assembly whereby user operation of the push/pull actuator from the resting position to the operative position is effects displacement of the latch slider assembly from its forward position to its rearward position.

13. A latch according to claim 12 wherein the latch slider assembly includes a bolt carriage and a carriage shuttle that is mounted for movement with the bolt carriage but arranged to permit relative displacement against a spring bias, and wherein the first push/pull actuator lever arm is arranged to act upon a surface of the bolt carriage and the 15 second push/pull actuator lever arm is arranged to act upon a surface of the carriage shuttle.

14. A latch according to claim 13 further including an entry lock mode mechanism having a privacy engagement member moveable between a first position and a second 20 position, wherein the privacy engagement member when in the second position engages with the carriage shuttle to prevent displacement of the latch slider assembly by the second push/pull actuator.

15. A latch according to claim 14 wherein entry lock mode selection mechanism 25 includes a user operable privacy pin coupled to the privacy engagement member to enable movement of the privacy engagement member between the first and second positions.

16. A latch according to any preceding claim wherein the first and second locking 30 devices each include a respective key-operated lock cylinder. – 29 –

17. A latch according to claim 16 wherein the first and second lock cylinders are arranged to opposite sides of the latching mechanism with respect to the direction of movement of the latch bolt. 5

18. A latch according to claim 17 as appended directly or indirectly to claim 2 wherein the first and second lock cylinders are coupled to engage with the latch slider assembly of the latching mechanism by way of respective rack and pinion mechanisms.

19. A latch according to claim 18 wherein the latch slider assembly includes a gear 10 shuttle having first and second rack gear formations disposed to opposite sides thereof.

20. A latch according to claim 19 wherein the first and second lock cylinders are fitted with respective concentric shuttle pinion gears arranged to engage with the respective first and second rack gear formations of the gear shuttle.

21. A latch according to claim 19 or 20 wherein the latch slider assembly includes at least one ball bearing carried by the gear shuttle and arranged to lock the latch slider assembly in its forward position by displacement of the gear shuttle by means of user rotation of one of the first and second lock cylinders.

22. A latch for a hinged or pivoting door, comprising: a housing adapted for mounting in or on a door; a latching mechanism supported by the housing, the latching mechanism including: 25 a latch bolt for reciprocating movement between an extended position and a retracted position, the latch bolt including a bolt head having a magnetic component wherein the latch bolt is operatively drawn to its extended position by magnetic force when the bolt head in use aligns with a magnetically susceptible strike member mounted on a corresponding door fixture, and 30 a latch slider assembly supported by the housing for reciprocating movement between a forward position and a rearward position, and wherein the latch slider assembly is coupled to the latch bolt by way of a rack and pinion mechanism; – 30 – first and second actuators disposed to opposite sides of the door, each of the first and second actuators being coupled to the latching mechanism to effect withdrawal of the latch bolt from its extended position to its retracted position upon operation by a user; and first and second locking devices disposed to opposite sides of the door, each of 5 the first and second locking devices being coupled to the latching mechanism to lock the bolt in its extended position upon operation by a user.

23. A latch mechanism for a hinged or pivoting door, comprising: a housing adapted for mounting in or on a door; 10 a latch slider supported by the housing for reciprocating movement between an extended position and a retracted position; at least one user operable actuator capable of driving the latch slider from the extended position to the retracted position; a latch bolt supported by the housing for reciprocating movement between an 15 extended position and a retracted position and coupled to the latch slider my means of a rack and pinion gear mechanism, the latch bolt including a bolt head having a magnetic component; wherein the latch bolt is operatively drawn to its extended position by magnetic force when the bolt head in use aligns with a magnetically susceptible strike member 20 mounted on a corresponding door fixture. – 31 –