IMPROVEMENTS IN MORTICE LATCHES

Abstract: A latch has a casing (1); a latch bolt assembly mounted in the casing and comprising a latch bolt head (5) and a latch bolt spindle (6); a follower assembly comprising a follower core (16) designed to receive the spindle of a handle, follower arms (21a, 24a) mounted on the follower core (16) and a link (11) arranged to be engaged by the follower arms (21a, 24a) and to be engaged with the latch bolt spindle (6); and a follower spring (27)arranged to act on the link (11). The spring (27) is mounted on a rod (28) which is arranged to act on the link (11). The spring (27) is mounted on a rod (28) which is arranged to extend into the casing. The rod (28) has an enlarged diameter portion (29)from which bayonet prongs (30) extend radially outwards. The rod (28) with the spring (27) mounted thereon extends through a bore (33) in a plate (32) mounted in the casing. Slots (34) extend radially outwards from the bore (33) and the bayonet prongs (30) can pass through the slots (34). The rod (28) is accessible from outside the casing through an aperture in the rear casing wall (36) whereby the rod can be engaged through said aperture and withdrawn from the casing through the aperture. The spring (27) is withdrawn with the rod (28) so that it can be changed for a stronger or weaker spring. In this manner, the strength of the spring can be chosen to meet the requirements of the latch and the spring can be changed without having to open the casing.

Description: IMPROVEMENTS IN MORTICE LATCHES THIS INVENTION relates to mortice latches and is particularly concerned with springing for the handles of mortice latches. 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 lock 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 lock or a combination of both. A problem encountered with conventional latches when used with unsprung door furniture is that the force of e 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 look sunsightly but it can also mean that, in some case, 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. 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. , The present invention seeks to solve the problem by providing a latch having means for changing the following spring without necessitating the opening of the latch casing. According to the invention, there is provided a latch having a casing, a latch bolt mounted in the casing, a latch bolt head mounted on the latch bolt, a follower arranged to engage the latch bolt and designed to eceive ~ the " spinτdle ' of a " handle ~ and ~ a- ~ spring ~ arranged to" act ~ on ~ the ~ follower, wherein the spring is mounted on 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 said casing whereby 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. 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 side elevation of one embodiment of part of a mortice latch according to the invention with the casing lid removed to show the internal components; Fig. 2 is a section taken on the line II-II in Fig. 1 ; and Fig. 3 is an exploded perspective view of components of the mortice latch shown in Figs. 1 and 2. In the drawings, like parts are denoted by like reference numerals. Referring to the drawings, a latch according to the invention comprises a casing 1 to one side of which is mounted an inner forend 3 and an outer forend 4. The casing is arranged to be closed by an opposite side cover plate 2. A latch bolt assembly is reciprocally mounted in the casing and comprises a latch bolt head 5 secured to a latch bolt spindle 6 by a cross pin 7 which engages in aligned bores 5a and 6a in the latch bolt head 5 and latch bolt spindle 6 respectively. The latch bolt head 5 is urged by a spring 8 to project through apertures in the fordends 3, 4 under normal conditions, the spring bearing at one end of the latch bolt head 5 and at the other end against a latch bolt spindle guide 10, a washer 9 being interposed between the spring 8 and guide 10. The spring 8 takes the form of a coil spring which is mounted on the spindle 6. The guide 10 is fixedly mounted in the casing 1 and has a cut out region 10a through which the spindle 6 extends. A substantially U-shaped link 11 is slidably mounted in the casing, the link being guided for, sliding movement by a guide pin 12 which is secured to one arm of the link 11 and extends into a slot 20 in the wall of the casing 1. The purpose of the slot is not only to guide sliding movement of the link but also to limit the extent of movement of the link. The latch bolt spindle 6 extends through an aperture 13 in the cross web 1 la of the U-shaped link 11 and a coil spring 25 mounted on the spindle 6 bears at one end against the cross web 1 la of the U-shaped link ~ l ~ l ~ and ~ a1rthe- other-end- against- an-enlarged-head portion 6b-of-the— spindle 6 . . The end of the head 6b is provided with screw slots 6c for engagement by a screw-driver or like implement. A follower core 16 is pivotally mounted in the casing, said follower core having a square-sectioned bore for the reception of a square-sectioned spindle of a latch handle (not shown). The follower core 16 is located in the casing below the link 11 and is provided on one side with a shoulder projection 19. The follower core 16 further has a circular upstand 17 on each side surrounding the square-sectioned bore, said upstands bearing against raised flanges on the casing 1 and cover plate 2 to form a wide journal. An ear 18 extends radially outwards from each of the upstands 17. An inner follower 21 having a follower arm 2 la, a circular aperture 22 and a notch 23 extending radially therefrom is mounted on one of the upstands 17 with the ear 18 engaging in the notch 23 and a similar outer follower 24 having a follower arm 24a, a circular aperture 22 and a notch 23 extending radially therefrom is mounted on one of the upstands 17 with the ear 18 engaging in the notch 23 and a similar outer follower 24 having a follower arm 24a, a circular aperture 25 and a notch 26 extending radially therefrom is mounted on the other upstand 17 this time with the ear 18 engaging in the notch 26. In the assembled condition of the latch, the arms 21a and 241 straddle the spindle 6 and press respectively against surfaces 11a of both legs of the U-shaped link 11. The link 11 is provided with a peg 14 for locating one end of a follower spring 27. The spring 27 takes the form of a coil spring which is mounted on a guide in the form of a rod 28 having a head 29 from which bayonet prongs 30 extend radially outwardly therefrom. The end surface of the head 29 is provided with slots 31 for engagement by a screw-driver or like implement. A spring retainer control plate 32 is mounted in the casing and has a circular aperture 33 from which slots 34 extend radially outwards. The guide 28 with the spring 27 mounted thereon can be inserted into the casing, through an aperture in a rear wall 36 of the casing which stands opposite the forends 3 and 4, said aperture being aligned with the aperture 33 in the plate 32. The guide 28 thus passes through said aperture 33 with the bayonet prongs 30 aligned with the slots 34 so that the prongs can pass through the plate 32. The spring 27 is compressed between the head 29 of guide 28, and the peg 14 located on the link 11. By rotating the slotted head 29 of the guide 28 with a screwdriver or similar tool the prongs 30 become misaligned with the slots 34 whereupon the spring 27 will force the prongs 30 against the plate 32. At the same time, the spring 27 will force the legs of the link 11 against the follower arms 21a and 24a which in turn act on the follower core 16 to force the shoulder projection 19 on the follower core against a screw column 35 mounted in the casing 1. In this manner handles (not shown) mounted on the ends of a square-sectioned spindle extending through the bore in the follower core 16 will be maintained in a substantially horizontal position by the force of the spring 27. Turning of one of the handles is effective to cause the follower core 16 to pivot in a clockwise direction as viewed in Fig. 1 which causes the follower arms 21a and 24a to move the link 11 to the right as viewed in Fig. 1 compressing the spring 27. At the same time, the cross web of the link 11 acts on the spring 15 and is effective to move the spindle 6 to the right as viewed in Fig. 1. This has the effect of moving the latch bolt head 5 to the right and of compressing the latch bolt return spring 8. The latch bolt head 5 is thereby retracted into the casing and the door or other openable member in which the latch is installed can be opened. If the handle is now released, the springs 8, 15 and 27 re-exert themselves and force the latch bolt head 5 once more to project outwardly from the casing. i The spring 8 can be a fairly light spring since it is merely needed to return the latch bolt head 5 to the position in which it projects from the fore ends 3 and 4. The spring 15 should be fairly heavy since it is required to transmit the movement of the link 11 to the spindle 6. The force of the spring 27 can be chosen to match the handles. If light or sprung handles are used, the spring 27 can be quite light but, if heavy or unsprung handles are used, the spring 27 should be heavy. The spring 27 can readily be changed, without opening the casing, simply by engaging the slots 31 in the head 29 of the guide 28 with a screw-driver or like tool which is passed through the aperture in the rear casing wall 36. The head 29 is then rotated until the prongs 30 are aligned with the slots 34 in the plate 32. The spring 27 is then allowed to expand to force the head 29 through the aperture in the rear wall 36 so that the guide 28 with the spring 27 can be removed from the casing. A different spring of a desired force to match thge handles intended for the latch can then be fitted on the guide 28 and the guide re-inserted into the casing in the manner above described. It will be seen that the above-described embodiment of mortice 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 |atch and can be changed if necessary for use with different handles without having to open the latch casing. The mortice latch according to the invention may, if desired, also be provided with a dead bolt assembly. Dead bolt assemblies which could be used with the mortice latch according to the present invention are disclosed in European Patent Specifications Nos. 0848125 and 0354634. Th e 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 bayonet type connection for the guide 28 may be replaced by a screw-threaded connection with the plate 32. The spring 27 is desirably a fairly tight fit on the guide 28 so that the spring will be withdrawn from the casing with the guide 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.

Claims: CLAIMS 1. A latch having a casing, a latch bolt mounted in the casing, a latch bolt head mounted oin the latch bolt, a follower arranged to engage the latch bolt and designed to receive the spindle of a handle and a spring arranged to act on the follower, wherein the spring is mounted on 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 said casing whereby 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. 2. A latch according to Claim 1, wherein the said member takes the form of a tube or rod or like elongate member. 3. A latch according to Claim 2, wherein the spring takes the form of a coil spring. 4. A latch according to Claim 2 or Claim 3, wherein the aperture in the casing takes the form of a bore in a wall of said casing. 5. A latch according to any one of the preceding claims, wherein the said member is provided with a bayonet connection which in engageable with a corresponding bayonet connection on engagement means in the casing. 6. A latch according to any one of Claims 1 to 4, wherein the said member is provided with an external screw thread which is engageable with an internal screw thread provided in engagement means in the casing. 7. A latch according to Claim 5 or Claim 6, 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. \ 8. A latch according to Claim 1, wherein the said member comprises a rod of circular cross-section adapted to receive the spring which comprises a coil spring, said rod having an enlarged diameter portion at one end against which one end of the coil spring is arranged to abut. 9. A latch according to Claim 8, wherein engagement means are provided on the enlarged diameter portion of the rod. 10. A latch according to Claim 9, wherein the engagement means comprise bayonet prons. 11. A latch according to Claim 9, wherein the engagement means comprise an external screw-thread. 12. A latch according to any one of Claims 8 to 11, wherein an end face of the rod is provided with at least one slot adapted to receive a screw-driver or like tool.

Inventors: MIDDLETON COLIN SIDNEY, MIDDLETON, COLIN, SIDNEY
Applicants: CARLISLE BRASS LTD, MIDDLETON COLIN SIDNEY, CARLISLE BRASS LIMITED, MIDDLETON, COLIN, SIDNEY
Application year: 2001
Main classification: E05B15
IPC codes: E05B15