WO2005106165A2

WO2005106165A2 - Improvements in mortice latches

Info

Publication number: WO2005106165A2
Application number: PCT/GB2005/001586
Authority: WO
Inventors: Colin Sidney Middleton
Original assignee: Colin Sidney Middleton
Priority date: 2004-04-27
Filing date: 2005-04-25
Publication date: 2005-11-10
Also published as: WO2005106165A3; GB2413591A; CN1969105A; GB2413591B; GB0508313D0; TW200602541A; GB0409384D0

Abstract

A mortice latch has a casing (1), a latch bolt lath (34) mounted in the casing, a latch bolt head (22) mounted on the latch bolt lath (34), a follower (36) arranged to engage the latch bolt lath (34) and designed to receive the spindle of a handle or knob, a spring (43) arranged to act on the follower (36) and a forend (29). One end of the spring (43) is engageable with a retainer (44) which is arranged to extend into the casing (1) to be releasably engaged within the casing and which is accessible from outside the casing through an aperture in the front side wall (2) of the casing (1). The arrangement is such that, after removal of the forend (29), the retainer (44) can be engaged through the aperture and withdrawn from the casing through the aperture, the spring (43) being withdrawn with the retainer (44) so that the spring can be changed without opening the casing (1) or without removing the casing from a door in which the said casing has been fitted.

Description

Improvements in Mortice Latches

This invention relates to mortice latches and is particularly concerned with springing for the handles of latch bolts.

It is usual for a conventional lever handle to be substantially horizontal when it is not in use. The handle can be turned in order to move a latch bolt into the latch casing in order for a door or like openable member, in which the latch is mounted, to be opened. When the handle is released, it is usually returned to its normal substantially horizontal position by the force of its own spring or, if unsprung, by the follower spring in the latch casing or a combination of both.

A problem encountered with conventional latches when used with unsprung door furniture is that the force of the spring must be matched to the weight of the handle. If a heavy handle is used, a heavy duty spring is called for since otherwise the force of the spring will be insufficient to return the handle to its normal substantially horizontal position and the handle will sag. This not only looks unsightly but it can also mean that, in some cases, the associated latch bolt may not be fully engaged in the socket in the frame surrounding the door or other openable member.

On the other hand, a light handle with its own spring calls for a light follower spring since, if a heavy duty spring is used, the handle is difficult to depress especially for people with age or disability problems.

The conventional answer to this problem is to open the latch casing and change the spring to one that matches the weight of the handle. This is however inconvenient and there is the risk of some of the components falling out of the latch casing entailing complicated and time-consuming re-assembly.

It has been proposed to provide a latch with means for adjusting the tension of the follower spring. However, it has been found in practice that the difference in tension required is so great that the adjustment is insufficient to meet the demands of light sprung handles and heavy unsprung handles.

One solution to this problem has been to provide a tube or rod extending into a latch casing on which the follower spring is mounted, said rod or tube being releasably engaged within the casing and being accessible from outside the casing through an aperture in the casing whereby the rod or tube can be engaged through the aperture and withdrawn from the casing through the aperture so that the following spring can be withdrawn from the casing through the same aperture and changed without having to open the casing.

While this attempt at solving the problem removes the necessity for opening the casing, it is still necessary to remove the casing from a door before the follower spring can be changed because the aperture has usually been provided in a rear side wall of the casing. Factory made doors with fitted locks and latches are becoming increasingly popular and it is inconvenient to have to remove a latch casing from a door in which it has been fitted in order to change the follower spring.

The present invention seeks to provide a further solution to the problem by means of a latch having means for changing the follower spring without necessitating opening of the latch casing or removing the casing from a door in which it has been fitted.

According to one aspect of the present invention, there is provided a latch having a casing, a latch bolt lath mounted in the casing, a latch bolt head mounted on the latch bolt lath, a follower arranged to engage the latch bolt lath and designed to receive the spindle of a handle or knob, a spring arranged to act on the follower and a forend, wherein one end of the spring is engageable with a member which is arranged to extend into the casing to be releasably engaged within the casing and which is accessible from outside the casing through an aperture in the front side wall of said casing whereby, after removal of the forend, said member can be engaged through said aperture and withdrawn from the casing through the aperture, the spring being withdrawn with said member so that the spring can be changed without opening the casing. After the spring has been changed, the member with a spring mounted thereon can be re-inserted into the casing through the aperture and re-engaged in the casing and the forend re-fitted to the casing.

It will be seen that, by means of the invention, the follower spring of a latch may be readily changed without having to open the casing or to remove the casing from a door in which it has been fitted. It is merely necessary to remove the forend which is accessible from the edge of the door in which the latch has been fitted.

According to one embodiment of the invention, the spring is arranged to act on the follower by means of a toothed rack which is slidably mounted in the casing, at least part of the surface of the follower being provided with a series of teeth which are arranged to engage with the teeth of the toothed rack and said toothed rack being engaged by the spring.

Another aspect of the invention provides a latch having a casing, a latch bolt lath mounted in the casing, a latch bolt head mounted on the latch bolt lath, a follower arranged to engage the latch bolt lath and designed to receive the spindle of a handle and a spring arranged to act on the follower, wherein the spring is arranged to act on a toothed rack which is slidably mounted in the latch casing and wherein at least part of the surface of the follower is provided with a series of teeth which are arranged to engage with the teeth of the toothed rack, the rack having a projection or recess adapted to receive one end of the follower spring and the other end of the spring being engageable with a member which is releasably engaged in the casing and which is accessible from outside the casing through an aperture in said casing.

Preferably, the said member takes the form of a tube or rod or like elongate member and the spring takes the form of a coil spring mounted thereon. In this case, the aperture in the casing desirably takes the form of a bore in the casing wall.

The rod, tube or like member may be provided with an external screw thread which is engageable with an internal screw thread provided on engagement means in the casing. Alternatively, the rod, tube or like member may be provided with a bayonet connection which is engageable with a corresponding bayonet connection on engagement means in the casing. The engagement means may take the form of a plate mounted in the casing and having a bore through which the spring can extend and with which the rod, tube or like member can engage.

According to a preferred embodiment of the invention, the said member comprises a rod of circular cross-section adapted to receive a coil spring and having a raised diameter portion at one end against which one end of the coil spring is arranged to abut. Engagement means such as an external screw-thread or bayonet prongs are desirably provided on the enlarged diameter portion of the rod and the end face of the rod is desirably provided with at least one slot adapted to receive a screw driver or like tool.

The invention will now be described in detail, by way of example, with reference to the drawings, in which :-

Fig. 1 is a front view of one embodiment of a mortice latch according to the invention;

Fig. 2 is a side elevation of the mortice latch shown in Fig. 1 with part of a cover plate for the latch casing cut away to show internal components; Fig. 3 is a side elevation of a second embodiment of a latch according to the invention with the casing cover removed and showing the latch bolt head in the withdrawn or retracted position and a dead bolt in the thrown position;

Fig. 4 is a side elevation of the latch shown in Fig. 3 but with the outer forend removed and with the dead bolt in the withdrawn or retracted position; and

Fig. 5 is a side elevation of a third embodiment of a latch according to the invention again with the cover removed but showing both the latch and the dead bolt in the thrown positions.

In the drawings, like parts are denoted by like reference numerals.

Reference will first be made to Figs. 1 and 2 of the drawings in which a mortice latch according to the invention comprises a casing 1 having a cover plate 4. Secured to one side wall 2 of the casing 1 is an inner forend in the form of a plate 26 and secured to the inner forend 26 by screws 28 is an outer forend in the form of a plate 29. Pillars are secured to the casing 1 and project upwardly therefrom, the pillars being internally screw-threaded, and the cover plate 4 is provided with apertures which are aligned with the screw-threaded bores in the pillars whereby the cover plate can be detachably secured to the casing 1 by means of screws 5. The inner forend 26 is provided with further bores 30 by means of which the inner forend can be secured to a door by screws 31 passing through said bores.

A deadbolt 6 is slidably mounted in the casing and is arranged to extend through guides in the side wall 2 of the casing 1 and in the inner forend 26 and outer forend 29. The deadbolt 6 is arranged to be operated by a cylinder lock 7 which extends through the casing 1.

A handle follower 8 extends through the casing 1 and is adapted to receive the spindle of a door handle (not shown). An arm 9 of the follower 8 carries a peg 10 which is arranged to engage with a lever 11 pivo tally mounted on a pillar 12 in the casing 1. The lever is arranged to act on a latch bolt lath (not shown) to which is connected a latch bolt head 22. The arrangement is such that turning the follower 8 in a clockwise direction as viewed in Fig. 2 is effective to act on the latch bolt lath and to retract the latch bolt head 22 into the casing 1.

The follower 8 is further provided on its periphery with a series of teeth 39 which are arranged to engage with a toothed rack 41 which is slidably mounted on a guide 42 in the casing 1. The rack 41 is provided at one end, which faces the side wall 2 at the front of the casing 1, with a spigot 47 which is adapted to receive one end of a coiled follower spring 43. The other end of the spring 43 is arranged to engage with a spigot 48 formed on a spring guide retainer 44. The retainer 44 is engaged with a spring retainer control plate 45 which is mounted in the casing 1. The control plate has a bore which may be screw-threaded to engage with a corresponding screw-thread on the retainer 44. The outer end of the retainer 44 is formed with a flange 49 in the outer surface of which a screw slot 50 is provided.

When the follower 8 is turned in a clockwise direction (as viewed in Fig. 2) to retract the latch bolt head 22, the engagement of the teeth 39 with the toothed rack 41 will move the rack to the left as viewed in Fig. 2 to compress the follower spring 43. The follower will normally be turned by a handle and if the handle is now released, the follower spring 43 will re-exert itself to move the rack 41 to the right as viewed in Fig. 2. This will cause the follower 8 to turn in an anticlockwise direction as viewed in Fig. 2 by virtue of the engagement of the teeth 39 on the follower 8 with the toothed rack 41. This turning movement of the follower 8 will cause the lever linkage 11 to allow the latch bolt lath to return to the position in which the latch bolt head 22 is in the extended position as shown in Fig. 2 of the drawings under the action of a latch bolt spring (not shown).

A bore 32 is provided in the inner forend 26 through which the retainer 44 is accessible when the outer forend 29 is removed from the inner forend. The screw slot 50 can now be engaged by a screw driver or other suitable tool and the retainer 44 can simply be unscrewed from the bore in the retainer control plate 45. The spring 43 is extracted from the casing with the retainer 44 and the spring can then be replaced by a lighter or a heavier spring, according to requirements, to match the handles which are to be fitted. The retainer 44 with the new spring fitted thereon can then simply be re-fitted in the casing by passing it through the bore 32 in the inner forend 26 and engaging it with the screw-threaded bore in the retainer control plate 45. A part of the side wall 2 of the casing 1 is cut away in the region of the retainer 44, as shown in Fig. 2, to permit the retainer 44 and the spring 43 to be taken out of the casing without removing the cover plate 4. Once the spring 43 has been changed and the retainer 44 has been re-fitted in the casing 1, the outer forend 29 can be re-fitted to the inner forend 26 by means of the screws 28.

Turning now to Figs. 3 and 4 of the drawings, this embodiment has a latch bolt lath 34 which has a central slot 16 which is located over a guidance peg 17 secured to the casing 1. Further guidance of the latch bolt lath 34 is achieved by a projection 18 which extends through an aperture in the side wall 2 of the casing 1 into an aperture 27 in the inner forend 26. The latch bolt lath 34 is provided with a flange 19 at its front end and a spindle 21 is rotatably mounted in an aperture in the flange 19. A latch bolt head 22 is secured to one end of the spindle 21 by a salop pin 23 and the other end of the spindle is shaped to locate one end of a latch bolt spring 24. The other end of the spring 24 engages with a shaped protrusion 25 which can either extend from the casing 1 or be formed on the guidance peg 17. When installed, the latch bolt head 22 projects from the casing through aligned apertures in the side wall 2, inner forend 26 and outer forend 27.

The latch bolt lath 34 also has an upstand 35 which extends perpendicularly to the plane of the latch bolt lath 34 at the end remote from the latch bolt head 22. The upstand 35 is engaged by an arm 37 extending from a handle follower 36. The follower 36 has a square bore 38 for the reception of a spindle (not shown) on which handles (not shown) may be mounted. The follower 36 is further provided on its periphery with a series of teeth 39 which are arranged to engage with a toothed rack 41 which is slidably mounted in a guide 42 in the casing 1. The guide 42 is secured to the base of the casing 1. A follower spring 43, located on a spigot 48 on a retainer 44 mounted on a retainer control plate 45 extending from the base of the casing 1, is arranged to act on one end of the toothed rack 41 to urge the follower 36 to a position in which the follower arm 37 is in the position "A" in Fig. 3 of the drawings. The upstand 35 on the latch bolt lath 34 will normally be held in engagement with the follower arm 37 by the action of the latch bolt spring 24 in which position the latch bolt head 22 will extend through the inner forend 26 and outer forend 29. This position is not shown in the drawings.

If a handle mounted on a spindle located in the bore 38 of the follower 36 is turned, the follower will pivot in a clockwise direction as viewed in Fig. 3 to move the toothed rack 41 to the left as viewed in Fig. 3 to compress the spring 43. At the same time, the engagement of the follower arm 37 with the upstand 35 will cause the latch bolt lath 34 to move to the right as viewed in Fig. 3 until the upstand 35 engages a nib 46 extending upwardly from the base of the casing 1. In this position, the latch bolt head 22 is fully withdrawn or retracted into the casing to the position shown in Fig. 3 of the drawings and the follower arm 37 is in the position marked "B" in Fig. 3. If the handle is now released, the follower spring 43 will re-exert itself to move the toothed rack 41 to the right as viewed in Fig. 3 which, by virtue of the teeth 39 on the follower 36, will cause the follower to pivot in an anti-clockwise direction as viewed in Fig. 3 to return the follower arm 37 to the position marked "A" in Fig. 3. At the same time, the latch bolt spring 24 will return the latch bolt head 22 to the thrown or extended position and the upstand 35 on the latch bolt lath 34 will be held in engagement with the follower arm 37.

The latch bolt lath 34 is provided with a projection 18 which can pass through an aperture 27 in the inner forend 26 and which normally engages the outer forend 29 to limit the extension of the latch bolt head 22 from the casing. The latch bolt head can be reversed by unscrewing the screws 28 to remove the outer forend 29. The projection 18 will then extend through the inner forend 26, as shown in Fig. 4 of the drawings, and the latch bolt head 22 will be clear of the inner forend so that the latch bolt head can be reversed simply by turning it through 180° because the spindle 21 on which the latch bolt head 22 is mounted is rotably mounted in the latch bolt lath 34. The outer forend 29 can then be refitted and its engagement with the projection 18 will force the projection back into the casing 1 and the latch bolt head 22 will then be located in an aperture in the inner forend 26 to prevent rotation of the latch bolt head.

The latch shown in Figs. 3 and 4 of the drawings also has a dead bolt 6 which is arranged to be operated by a cylinder lock 7. The dead bolt 6 is slidably mounted in the casing 1 and extends through aligned apertures in the side wall 2 of the casing 1, the inner forend 26 and the outer forend 29. The dead bolt has a dead bolt lath 61 provided with a guidance slot 62 and a pair of notches 65 and 66. A pair of posts 67 and 68 extend upwardly from the base of the casing 1 and are located in the guidance slot 62 of the dead both lath 61 for the purpose of guiding the sliding action of the dead bolt 6. A plate 72 is slidably mounted in the casing 1 and is provided with slots 73 and 74 and an arcuate surface 75. The post 68 extends through one of the slots 73 and a further post 69 mounted on the base of the casing 1 extends through the other slot 74. When installed in the casing, the arcuate surface 75 will be located at the lower edge of the plate 72 which plate further has an upstand 76 which is engageable in the notches 65 and 66 in the dead bolt lath 61. The upstand 76 engages in the notch 65 in the thrown or extended position of the dead bolt 6 shown in Fig. 3 and in the notch 66 in the withdrawn or retracted position of the dead bolt shown in Fig. 4 of the drawings. The plate 72 is urged in a downwards direction by a coil spring 78 bearing at one end against the plate 72 and at the other end against the guide 42 for the toothed rack 41. The spring 78 is located in a socket 79 in the guide 42 and on a peg 77 on the plate 72. A lever 81 is pivotally mounted on a post 82 in the casing and is arranged to engage a rear surface of the dead bolt 6. The cylinder lock 7 (not shown in Fig. 4) is held in position in the casing 1 by a screw 83 which passes through apertures in the inner forend 26 and side wall 2 of the casing and engages with a screw threaded bore in a block 84 which is secured to the base of the casing 1. The dead bolt can be moved from the withdrawn or retracted position shown in Fig. 4 of the drawings to the extended or thrown position shown in Fig. 3 by inserting a key into the cylinder lock 7 and turning the key in an anti-clockwise direction as viewed in the drawings. This has the effect of turning a cam 71 of the cylinder lock in an anti-clockwise direction and the cam 71 will initially engage the plate 72 and move said plate upwards against the force of the spring 78. This movement will cause the upstand 76 to move out of notch 66 in the dead bolt lath 61. At the same time, the cam 71 enters a recess 70 in the dead bolt lath 61 and continued rotational movement of the cam 71 will move the dead bolt lath 61 to the left as viewed in Fig. 3 of the drawings. The cam 71 also engages the lever 81 which pivots about the post 82 and is effective to move the dead bolt 6 from the withdrawn position shown in Fig. 4 of the drawings to the thrown position shown in Fig. 3 of the drawings. As the dead bolt 6 reaches the thrown position, the cam 71 moves out of engagement with the plate 72. The spring 78 then re-exerts itself to move the upstand 76 on the plate 72 into the notch 65 to lock the dead bolt in the thrown position.

The dead bolt 6 can be moved from the thrown position shown in Fig. 3 of the drawings to the retracted position shown in Fig. 4 of the drawings by inserting a key into the cylinder lock 7 and turning the key in a clockwise direction as viewed in the drawings. This has the effect of turning the cam 71 in a clockwise direction and the cam will again engage the plate 72 and move the plate upwards against the action of the spring 78. This movement will cause the upstand 76 to move out of the notch 65 in the dead bolt lath 61. Continued turning of the key will move the cam 71 into the recess 70 in the dead bolt lath 61 and continued rotation of the cam 71 will move the lath bolt lath 61 to the right as viewed in Figs. 3 and 4 of the drawings. As the dead bolt 6 reaches the withdrawn position shown in Fig. 4 of the drawings, the cam 71 moves out of the recess 70 and out of contact with the plate 72. The spring 78 re-exerts itself to move the upstand 76 on the plate 72 into the notch 66 to lock the dead bolt in the retracted position. The latch bolt can also be operated by an extra turn of the key. A lever 85 is pivotally mounted on a lug 86 on the follower 36 and has an elongated slot 87 which is located on a pin 88 extending from the dead bolt lath 61. The lever 85 is provided at the end remote from its pivot point with an upstand 89. When the dead bolt has been moved by the cam 71 of the cylinder lock 7 to the retracted position and if the key is again turned in a clockwise direction, the cam 71 will engage the upstand 89 on the lever 85 and move the lever 85 upwards. The engagement of the pin 88 in the slot 87 serves to guide the lever and as the lever moves upwards it causes the follower 36 to rotate in a clockwise direction, as viewed in Fig. 4, which causes the follower arm 37 to move the latch bolt lath 34 to the right, by virtue of the engagement of the upstand 35 by the follower arm 37, and thus retract the latch bolt head 22. The key can then be turned back so that the cam 71 is disengaged from the upstand 89 and the follower 36 can be returned to its normal position under the action of the follower spring 43.

Handle operation of the follower 36 to retract the latch bolt head 22 has no effect on the dead bolt because as the follower 36 is pivoted, the lever 85 is free to move with the follower because the elongated slot 87 in the lever 85 is free to move along the pin 88.

As with the embodiment shown in Figs. 1 and 2 of the drawings, the inner forend 26 is provided with a bore 32 through which the retainer 44 is accessible when the outer forend 29 is removed from the inner forend 26. The outer end of the retainer 44 is formed with a flange 49 in the outer surface of which a screw slot is provided. Once the outer forend has been removed, the screw slot in the flange 49 of the retainer 44 is accessible through the bore 32 in the inner forend 26 and can be engaged by a screw driver or other suitable tool and the retainer 44 can simply be unscrewed from the bore in the retainer control plate 45. The spring 43, one end of which is mounted on a spigot 48 projecting from the retainer 44, is extracted from the casing with the retainer 44 and the spring can be replaced by a lighter or heavier spring according to requirements. The retainer 44 fitted with the new spring can then be re-fitted in the casing by passing it through the bore 32 in the inner forend 26 and engaging it with the retainer control plate 45. Once the spring has been changed and the retainer 44 has been re-fitted in the casing 1, the outer forend 29 can then be re-fitted to the inner forend 26 by means of the screws 28.

The embodiment shown in Fig. 5 of the drawings differs from the embodiments shown in Figs. 1 and 2 and in Figs. 3 and 4 in a number of respects. In this embodiment, the latch bolt lath 94 does not have a projection similar to the projection 18 of the other embodiments but it does have an upstand 95 which is engaged by a follower arm 37 of a handle follower 36. The follower 36 is also provided with a series of teeth 39 arranged to engage with a toothed rack 41 which is slidably mounted in a guide 42 in the casing 1. A follower spring 43 acts on the toothed rack 41 as in the embodiment of Figs. 3 and 4. The spring 43 serves to act on the follower 36 to cause said follower to rotate in an anti-clockwise direction as viewed in Fig. 5, rotation of the follower being restricted by a spindle 98 which engages the follower arm 37.

In this embodiment, the follower spring 43 is located in a recessed bore 40 in the toothed rack 41 and its other end is engaged on a spigot 51 on a retainer 52. The retainer 52 is provided with prongs which are engageable with a fitting 53 on the side wall 2 of the casing in the manner of a bayonet connection. The outer face of the retainer 52 is provided with a screw-slot to enable it to be turned and, when fitted, the majority of the retainer 52 is located in a bore 32 in the inner forend 26. If it is desired to change the follower spring 43, the outer forend 29 is removed as before and the screw slot in the retainer 52 is engaged by a tool to turn the retainer and to disengage its prongs from the fitting 53. The retainer 52 with the spring 43 mounted thereon can then be withdrawn from the casing and the spring can be changed for a lighter or heavier spring as desired. The retainer 52 fitted with the new spring can then be re-fitted in the casing by passing the spring through the bore 32 in the inner forend 26 until the inner end of the spring is located in the recessed bore 40 in the toothed rack 41. The spring is then compressed until the retainer 52 is located in the bore 32 in the inner forend 26 when the retainer is turned so that its prongs are again engaged with the fitting 53. The outer forend can then be refitted to the inner forend 26 by means of the screws 28.

The latch bolt head 22 can be moved from the extended position shown in Fig. 5 to the withdrawn or retracted position by turning a handle fitted to an end of a spindle (not shown) extending through a square bore 38 in the follower 36. This has the effect of causing the follower arm 37 to pivot to move the latch bolt lath 94 to the right as viewed in Fig. 5 by virtue of the engagement of the upstand 95 by the follower arm 37. Movement of the latch bolt 22 is continued until a shoulder 96 on the latch bolt lath 94 engages a post 97 projecting from the base of the casing 1. At the same time as the latch bolt is moved to the right, the toothed rack 41 is moved to the left as seen in Fig. 5 to compress the follower spring 43. Release of the handle enables the spring 43 to re-exert itself to return the follower 36 and the latch bolt to the positions shown in Fig. 5 of the drawings.

In this embodiment, the latch bolt head 22 can again be reversed simply by removing the outer forend 29. In this case, however, when the outer forend is removed, the spring 43 acting on the follower 36 via the toothed rack 41 will cause the follower arm 37 to move the spindle 98 partially out of the casing until the follower arm 37 is clear of the upstand 95 on the latch bolt lath 94. The spring 24 acting on the latch bolt is then effective to move the latch bolt head 22 clear of the inner forend 26. The latch bolt head 22 can then be reversed simply by turning it through 180° because the spindle 21 on which the latch bolt head is mounted is rotatably mounted in the latch bolt lath 94. The latch bolt head 22 must then be pushed back into the casing, against the force of the spring 24 and the outer forend 29 refitted so that the upstand 95 on the latch bolt lath 94 is again engaged by the follower aπn 37 because the spindle 98 again engages the follower arm 37.

The latch shown in Fig. 5 of the drawings also has a dead bolt 6 which is arranged to be operated by a multi-detainer lock operated by a key. The dead bolt has a dead bolt lath 101 provided with a slot 102 through which a post 99 mounted on the base of the casing 1 extends to provide guidance for the deadbolt. A stump 103 extends from the dead bolt lath 101 and is engaged by a number of detainers 106 (only one shown in Fig. 5). The detainers are pivotally mounted on a post 112 in the casing and each is urged by a respective leaf spring 111 into contact with an arcuate member 113 surrounding a key hole slot 114. A lever 115, pivotally mounted on a post 116 which is secured to the base of the casing 1, is arranged to bear against a shoulder 105 on the dead bolt lath 101 and is arranged to be engaged by a key in a manner to be hereinafter described. A circular disc 117 surrounds the arcuate member 113 and has a peripheral depression 118 which is engaged by a curved end of a spring 121 which is mounted on a post 122 secured to the base of the casing 1, the other end of the spring 121 bearing against a side wall of the casing 1.

Fig. 5 shows the dead bolt 6 in the thrown or extended position. In order to withdraw the dead bolt 6 into the casing 1, it is necessary to insert a key into the key hole slot 114 and turn the key in a clockwise direction as viewed in Fig. 5. As the key is rotated, it will first engage the detainers 106 and lift them against the action of the detainer springs 111. The detainers are moved to a position in which the stump 103 on the dead bolt lath can enter a gate 107 in the detainer 106. At the same time, the key enters a recess 104 in the dead bolt lath 101 and engages the dead bolt lath 101. Further rotation of the key causes the dead bolt lath 101 to move to the right as viewed in Fig. 5, by virtue of the engagement in the recess 104 by the key, so that the stump 103 moves along the gates 107 in the detainers 106. This movement is continued until the outer end of the dead bolt 6 is flush with the outer forend 129 at which point the key breaks contact with the dead bolt lath 101 and the detainers 106. The gates 107 are each provided with a respective notch 108 at the inner end and as the key breaks off engagement with the detainers 106, the springs 111 are effective to cause the detainers 106 to pivot downwardly so that the stump 103 on the dead bolt lath 101 engages in the notches 108 and the dead bolt is held in the withdrawn position. Rotation of the key is continued until the keyhole slot is returned to the position shown in Fig. 5 of the drawings when the key can be removed from the lock. Although only one detainer 106 is shown in Fig. 5, it will be appreciated that the lock will in fact be provided with more than one detainer, the usual member being five although more or less detainers may be provided as desired.

In order to move the deadbolt to the thrown or extended position, the key must first be inserted into the key hole slot 114 and the key turned in an anti-clockwise direction as viewed in Fig. 5 of the drawings. The key will first engage the detainers 106 and lift them so that the notch 108 is moved clear of the stump 103. At the same time, the key enters the recess 104 in the dead bolt lath 101 and moves the lath and hence the dead bolt 6 to the left as viewed in Fig. 6. With continued rotation, the key engages the lever 115 which bears against the shoulder 105 of the dead bolt lath and because of its changing angle increases the throw of the dead bolt. Further rotation of the key moves it out of engagement with the lever 115 and with the detainers 106. The springs 111 can therefore cause the associated detainers 106 to pivot downwardly to engage with the stump 103 and secure the dead bolt in its thrown position as shown in Fig. 5 of the drawings.

It will be seen that the latch according to the invention will overcome the problems of the prior latches in that the return spring can be readily matched to the associated handles which are to be used with the latch and can be changed if necessary for use with different handles without having to open the latch casing and without having to remove the latch casing from a door in which the casing has been fitted.

The invention is not restricted to the above-described embodiment but modifications and variations may be made without departing from the scope of the invention. For example, the screw-threaded connection for the retainer 44 may be replaced by a bayonet type connection 52,53 as shown in Fig. 5 of the drawings. The spring 43 is desirably a fairly tight fit on the spigot so that the spring will be withdrawn from the casing with the retainer 44 and there is no fear of the spring falling off and into the casing which would entail removal of the cover plate to extract it. Further, instead of being operated by a cylinder lock, the dead bolt could be operated by a lever security system.

Claims

1. A latch having a casing, a latch bolt lath mounted in the casing, a latch bolt head mounted on the latch bolt lath, a follower arranged to engage the latch bolt lath and designed to receive the spindle of a handle or knob, a spring arranged to act on the follower and a forend, wherein one end of the spring is engageable with a member which is arranged to extend into the casing to be releasably engaged within the casing and which is accessible from outside the casing through an aperture in the front side wall of the casing whereby, after removal of the forend, said member can be engaged through said aperture, the spring being withdrawn with said member so that the spring can be changed without opening the casing.

2. A latch according to claim 1, wherein the spring is arranged to act on the follower by means of a toothed rack which is slidably mounted in the casing, at least part of the surface of the follower being provided with a series of teeth which are arranged to engage with the teeth of the toothed rack and said toothed rack being engaged by the spring.

3. A latch according to claim 2, wherein the toothed rack has a projection adapted to receive the other end of the spring.

4. A latch according to claim 2, wherein the toothed rack is provided with a closed bore or recess adapted to receive the other end of the spring.

5. A latch having a casing, a latch bolt lath mounted in the casing, a latch bolt head mounted on the latch bolt lath, a follower arranged to engage the latch bolt lath and designed to receive the spindle of a handle and a follower spring arranged to act on the follower, wherein the spring is arranged to act on a toothed rack which is slidably mounted in the casing and wherein at least part of the surface of the follower is provided with a series of teeth which are arranged to engage with the teeth of the toothed rack, the rack having a projection or recess adapted to receive one end of the follower spring and the other end of the spring being engageable with a member which is releasably engaged in the casing and which is accessible from outside the casing through an aperture in the casing.

6. A latch according to any one of the preceding claims, wherein the said member is provided with an external screw-thread which is engageable with an internal screw-thread provided on engagement means in the casing.

7. A latch according to any one of claims 1 to 5, wherein the said member is provided with a bayonet connection which is engageable with a corresponding bayonet connection provided on engagement means in the casing.

8. A latch according to claim 6 or claim 7, wherein the engagement means take the form of a plate mounted in the casing and having a bore through which the spring can extend and with which the said member can engage.

9. A latch according to any one of the preceding claims, wherein the said member takes the form of a tube or rod or like elongate member.

10. A latch according to any one of claims 1 to 5, wherein the said member comprises a rod of circular cross-section adapted to receive the spring and having a raised diameter portion against which the said one end of the spring is arranged to abut.

11. A latch according to claim 10, wherein engagement means are provided on the enlarged diameter portion of the rod.

12. A latch according to claim 11, wherein the engagement means comprise an external screw-thread or bayonet prongs provided on the enlarged diameter portion of the rod and engageable with an internal screw-thread or bayonet recesses provided in corresponding engagement means which are mounted in the casing.

13. A latch according to claim 12, wherein the engagement means in the casing take the form of a plate mounted on the base of the casing and having a bore through which the spring can pass and with which the engagement means on the enlarged diameter portion of the rod can engage.

14. A latch according to any one of the preceding claims, wherein the spring is a coil spring.

15. A latch substantially as described herein with reference to Figs. 1 and 2 or Figs. 3 and 4 or Fig. 5 of the drawings.