Door latches

Abstract

 The present invention provides a door latch comprising a tongue (2) having a projecting position for latching a door, a handle shaft (1) having a longitudinal axis, at least one handle which acts on the handle shaft (1) and means (3,5,46) for transmitting motion of the shaft (1) to the tongue (2), whereby the tongue (2) can be retracted from its projecting position to unlatch the door in at least two modes including moving the handle along the said axis, and rotating the handle with respect to the said axis.
Many variations of the means (3-3, 5, 46) for transmitting motion of the shaft (1) are disclosed. Some of these variations use the conventional D-lever component (46) alone, some use that component with additional components and further embodiments avoid use of a D-lever altogether.
Disclosure is made of arrangements in which the extent of projection of the tongue (2) from the body of the latch is variable. Optional selector means (9, 37) are provided so as to produce an "either-or" effect between the push-pull and turn modes of operation. A catch (51-61) which retains the tongue (2) in its retracted position when the door is open is also described. The catch (51-61) can be automatically released upon closure of the door.

Description

[0001] The present invention relates to door latches and in particular to latches of the type in which a tongue is withdrawn from postive engagement with a retaining member by relative motion between a handle and the door.

[0002] Conventional latches of this general type comprise a handle which is rotated in order to retract the tongue against its biasing and unlatch the door. This form of conventional latch will be referred to herein as a "turn" latch. The turn latch requires the handle to be rotated and a subsequent push or pull motion to be applied to the door in order to unlatch and open the door.

[0003] The latch tongue is resiliently biased to project from the edge of the door. Consequently, in order to close the door it is normal to rotate the handle again and push or pull the door. Absence of rotation of the handle will result in the latch tongue striking against the door post.

[0004] The requirement to rotate the handle has been mitigated to some extent by shaping one face of the tongue so as to co-operate with an inclined portion of a guard plate which surrounds the tongue retaining recess in the door post. The tongue rides over the incline as the door doses and the tongue is thereby retracted into the door against its bias. When the door is finally closed the tongue is propelled into the door post recess and the door is thereby latched.

[0005] With a view to mitigating at least one of the above-mentioned disadvantages the present invention provides a door latch comprising a tongue having a projecting povition for latching a door, a handle shaft having a longitudinal axis , at least one handle which acts on the handle shaft and means for transmitting motion of the shaft to the tongue, whereby the tongue can be retracted from its projecting position to unlatch the door in at least two modes including moving the handle along the said axis, and by rotating the handle with respect to the said axis.

[0006] According to a second aspect of the present invention there is provided a door latch comprising a body and a tongue which projects from the body into a projecting position for latching the door and which is retracted from the projecting position to unlatch the door, wherein the extent to which the tongue projects from the body when in the projecting position is variable.

[0007] According to a further aspect of the invention there is provided a door latch comprising a body and a tongue which projects from the body into a projecting position for latching the door and which is retracted from the projecting position to unlatch the door, the latch further comprising a handle shaft having g a longitudinal axis, at least one handle which acts on the handle shaft and means for transmitting motion of the shaft to the tongue, whereby the tongue is retracted from its projecting position to unlatch the door by moving the handle along the said axis and the extent to which the tongue projects from the body when in the projecting position is variable.

[0008] In connection with certain aspects of the present invention it is found beneficial to introduce means to control the distance by which the tongue projects from the end plate of the latch when the tongue is in the projecting position. This may be achieved if the tongue is formed of two components which are threadedly engaged such that the length of tongue projecting from the end plate of the latch when the tongue is in the projecting position is readily variable. In this way many of the actions .of opening and closing the door are facilitated and improved.

[0009] The first and third aspects of the present invention enable the door to be unlatched and opened with a single movement. Dependent upon from which side the door is opened it is only necessary to push or pull upon the handle in order to both unlatch the door and to continue opening the door. This form of latch can conveniently be referred to as a push-pull latch.

[0010] To avoid having frequently to repeat the phrase "pushing or pulling the handle as the case may be" most of the following description will be given with reference to operation from the pull-to-open side of the door. This is of course also the push-to- close side of the door.

[0011] The means for transmitting motion of the shaft to the tongue can be implemented in a relatively simple manner. Preferably, the said means includes a crank having two arms projecting from a spindle which is pivoted about a fixed axis.

[0012] The handle shaft and tongue are provided with respective formations and the act.on of the handle shaft formation upon one arm of the crank causes the crank to pivot and the other arm of the crank to act upon the formation associated with the tongue. The application of a pulling motion on the handle shaft therefore results in retraction of the tongue from its projecting position A number of alternative means of implementation are also disclosed.

[0013] The tongue can be resiliently biased into its projecting position. An alternative arrangement includes a tongue moving mechanism which avoids such resilient biasing.

[0014] In a preferred form the is provided with a catch which engages the retracted tongue as the door is opened and which retains the tongue in the retracted position until the door is closed.

[0015] Particular utility is imparted to the latch by an arrangement in which the latch retaining catch is automatically released when the door is closed.

[0016] The first aspect of the present invention combines the features of the push-pull latch with the features of the conventional turn latch so that the door may be unlatched and opened in the conventional handle rotation manner or in the simple pull-to-open manner of the push-pull latch. It is believed that this embodiment presents particular advantages especially relating to public acceptance of this new form of latch. The conventional turn type of latch has been known for such a length of time and without the introduction of any significant modifications that its operation has become almost instinctive for the majority of people.

[0017] Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:-

Figures 1A and 1B illustrate in plan view the handle shaft, tongue and crank of the latch, with the tongue in its projecting position and movement of the handle shaft to retract the tongue, respectively,

Figure 2 is a front elevation of the tongue including the tongue carriage,

Figures 3A and 38 are front and sectional elevations respectively of one half of the latch case with the end plate attached,

Figure 4 is a front elevation of the other case plate of the latch,

Figures 5A, 5B, 5C and 5D illustrate a front elevation, plan elevation and two sectional elevations of a shaft assembly bracket which forms part of the latch,

Figure 6A shows a plan view of the handle shaft by itself and figures 6B, 6C, 6D, 6E and 6F show the cross-sectional profile of the handle shaft at various positions along its length,

Figures 7A and 7B illustrate front and plan elevations respectively of a D-lever used in the latch,

Figures 8A and 8B show a pin and pin holder both in plan view, respectively,

Figure 8C is a front elevation of the pin holder of figure 8B and figure 8D is a sectional view relating to figure 8C,

Figure 8E is a sectional view related to figure 8C and also showing the case plates of the latch,

Figures 9A, 9B, 9C and 9D illustrate a catch cylinder and shaft, Figures 9A, 9B, and 9C being a front elevation, an end elevation and a plan elevation of the catch cylinder respectively and Figure 9D is a front elevation of the catch shaft;

Figures 10A, 10B and 10C show the operational relationship between the components of Figures 8 and 9 when the tongue is in its projecting position, the views are a front elevation, a plan elevation and an end elevation respectively,

Figures 11A, 11B and 11C correspond to Figures 10A, 10B and 10C, but illustrate the operational relationship of the components when the tongue is retracted from its fully projecting position;

Figure 12 is a vertical sectional front elevation of the assembled latch;

Figures 13A and 13B show a front elevation and a sectional elevation of a guard plate for use with the latch shown in Figure 12;

Figure 14 is a plan view of the handle shaft of an alternative embodiment;

Figure 15 is a schematic sectional front elevation of an assembled latch which employs an alternative crank mechanism;

Figure 16 shows part of the handle shaft having a modification enabling a simplified handle shaft to tongue carriage motion transfer mechanism to be implemented;

Figure 17 is a plan view of a handle shaft and a sectioned tongue carriage for a latch which avoids use of a crank mechanism;

Figure 18 is a plan view of the handle shaft of Figure 17 illustrating aspects of its cooperation with the support bracket of the latch; and

Figure 19 is a vertical sectional front elevation of a latch employing the arrangements of Figures 17 and 18.

[0018] Embodiments of a latch according to the present invention are illustrated in the accompanying drawings. These embodiments all illustrate latches incorporating both the push-pull and conventional "turn" modes of operation. It should however be appreciated that a simple push-pull latch can readily be prepared from the following description and drawings by omission of the features of the conventional turn latch. The remaining features of the push-pull latch can be significantly simplified in such an embodiment.

[0019] Similarly the description of the crank mechanism shown in Figures 1A and 1B is given in relation to a latch incorporating a catch mechanism. Many of the parts of this latch shown in Figure 12, for example, relate to this catch mechanism, and a simplified latch incorporating the push-pull and turn mechanisms can readily be prepared from the following description and drawings by ommission of the features of the catch.

[0020] Figures 1A and 1B serve to illustrate the basic operation of a push-pull latch. These figures show the handle shaft 1, tongue 2 and crank 3. The handle shaft 1 is held by a shaft assembly bracket 4 and the tongue 2 includes a tongue carriage 5. It will be appreciated that the handle shaft 1 extends through the thickness of the door and that the tongue 2 projects from the edge of the door. The handle shaft 1 can be displaced along its longitudinal axis and is resiliently biased into a rest position in which it is centered with the width of the door by the spring 6.

[0021] The crank 3 is formed from two arms 7 and 8 which are mutually perpendicular when viewed in plan view and which project perpendicularly from a spindle which is pivoted about a fixed axis. The free end of the arm 7 of crank 3 engages a formation 9 on the handle shaft 1. The pivot of the crank 3 forms part of the shaft assembly bracket 4 and the crank arm 8 passes through an aperture in the bracket 4 and engages a formation 10 on the tongue carriage 5.

[0022] Figure 1A shows the handle shaft 1 in its rest position and the tongue 2 in its projecting position. In this situation the crank arms 7 and 8 are parallel with the tongue carriage 5-and handle shaft 1, respectively. In order to retract the tongue 2 from its projecting position so as to unlatch the door the handle shaft 1 is displaced along its longitudinal axis. Displacement of the handle shaft 1 is by a push or pull action upon a handle (not shown) ,of which one is attached to either end of the shaft 1, in dependence upon from which side of the door the latch is being operated. Figure 1B shows the position of the components when the handle shaft 1 is displaced. The handle shaft 1 is displaced from its rest position against the action of the spring 6. The formation 9 of the shaft 1 abuts against a stop 11 provided by the shaft assembly bracket 4. Displacement of the handle shaft 1 is thereby limited. The arm 7 of crank 3 rotates about the pivot of the crank 3 due to the engagement between the arm 7 and the shaft formation 9. Consequently, the crank arm 8 rotates about the pivot of the crank 3 and by action of the arm 8 upon formation 10 of the tongue carriage 5, the tongue 2 is retracted into the door. The door is thereby unlatched.

[0023] It can be seen from Figure 2 that the tongue 2 is threadedly engaged with the tongue carriage 5. This enables the extent to which the tongue projects from the end plate of the latch when the tongue is in the projecting position to be varied. The provision of an adjustable tongue is particularly useful in pratice because the gap between the closed door and the door post is not the same in every case and indeed there may be considerable difference in this gap between one instance and another.

[0024] The adjustable tongue enables the distance the tongue projects to be suited to the actual gap between the door and the door post in each individual instance. When the latch is installed the tongue is adjusted so that it projects the correct distance to suit the gap and thereafter the adjustment is not normally altered. It will of course be necessary for the manufacturer to ensure that the threaded shaft of the tongue is sufficiently long so that the distance the tongue projects may be suited to the widest gap likely to be encountered.

[0025] The adjustable tongue offers a number of advantages which will now be explained.

[0026] The first advantage is in respect of opening the latch in the push-pull mode. In order to achieve a smooth and easy action when opening the door by pulling the handle it is necessary that the tongue should not overlap the guard plate attached to the door post by more than a comparatively small distance. If the overlap is increased then the additional friction will make opening the door in this way difficult. The additional friction arises because pulling the handle tends to press the tongue against the guard plate and the problem is therefore common to all latches in which the tongue may be retracted by pulling the handle irrespective of the particular mechanism by which the pulling force exerted on the handle is transmitted to the tongue carriage. In all latches of this kind it is necessary to ensure that the overlap between the tongue and the guard plate is kept small enough to control the friction so that the action may be smooth and easy. On the other hand the overlap must be sufficient to keep the door securely latched. The adjustable tongue makes it possible to ensure that the overlap is of the desired distance whether the gap between the door and door post is large or small. This is not possible if the tongue is fixedly attached to the tongue carriage.

[0027] The-second advantage of the adjustable tongue is that it makes possible an improvement to the design of the shaped rear face of the tongue itself. In ordilary latches the tongue is fixedly attached to the tongue carriage and, because of the uncertain gap between the closed door and the door post, it is not known in advance whereabouts along its length the rear face of the tongue will collide with the guard plate when the door is pushed closed without turning the handle. If the gap is large the tongue will collide with the guard plate near the tip of the tongue; and if the gap is small collision will occur near the root of the tongue. For this reason the slope of the rear face of the tongue must at present extend throughout most or all of the length of the tongue and so at any one point will be comparatively shallow. This will cause the shock and noise of impact to be comparatively great. However, in a latch with an adjustable tongue, when the tongue is adjusted so as to make the overlap with the guard plate comparatively small as explained in the description of the first advantage this will simultaneously ensure that the collision between the guard plate and the tongue will occur near the tip of the tongue.

[0028] Therefore only the part of the rear face of the tongue close to the tip will now need to be made with a slope. In consequence the slope may be made steeper, with the result that the shock and noise of impact between the tongue and the guard plate is greately reduced; and also with the result that the pressure from the guard plate on the sloping end of the tongue will more easily push the tongue inwards against the bias of the tongue carriage.

[0029] The fact that the tongue will now be adjusted to overlap the guard plate by a comparatively small distance, combined with the improved design of the rear face of the tongue itself, together greately improve the action of the latch when the door is pushed closed without first turning the handle. This improvement is particularly important in a latch with a push-pull mechanism for opening the door because it ensures that the complete cycle of operations may conveniently be completed without the necessity of turning the handle at any time. But the adjustable tongue also improves the action in the way explained when fitted to any latch wherein the tongue is outwardly biased including a conventional turn latch.

[0030] The third advantage of the adjustable tongue is that it makes possible an improvement in the design of the guard plate. In conventional latches, becuase of the comparatively large shock and noise of impact it is customary for the guard plate to be provided with a projection intended to receive and minimise the initial impact and also to cooperate with the shape rear face of the tongue in pushing the tongue inwards against the outwards bias. This projection from the guard plate extends forwards from the door post. It is thus somewhat unsightly and may be the cause of nuisance in that clothing or other articles may be caught thereon. However in a latch with an adjustable tongue the action of closing the door will be greately improved and it is therefore only necessary for the projection from the rectangular part of the guard plate to extend as far as the outer edge of the door post. The extension outwards beyond the door post is no longer necessary so that the appearance is improved and the possible cause of nuisance removed.

[0031] The fourth advantage of the adjustable tongue is in limiting the angle through which it is necessary to turn the handle in order to withdraw the tongue from the guard plate. When the tongue is adjusted so as to make the overlap with the guard plate comparatively small this will simultaneously ensure that it is only necessary to turn the handle through a comparatively small angle to retract the tongue and unlatch the door. Similarly if the door is standing open and a person wishes to ensure that the tongue does not strike against the guard plate when the door is being closed it will now only be necessary to turn the handle through a comparatively small angle. Thus the adjustable tongue ensures that the two actions referred to will always be easy and convenient. This is compared to the case in which a latch has the tongue fixedly attached to the tongue carriage and in which the gap between the door and the door post is small, in which case it will be necessary to turn the handle through a comparatively large angle for either of the purposes mentioned.

[0032] The fourth advantage of the adjustable tongue may be utilised in any latch in which the tongue is outwardly biassed and in which there is an ability to retract the tongue against the bias by turning the handle including the combined latch and including the conventional turn latch.

[0033] It is pointed out that the four advantages of the adjustable tongue described above are all consonant with each other in that each depends on the overlap of the tongue with the guard plate being adjusted so as to be comparatively small.

[0034] It is also pointed out that it is not possible to describe the advantage of the adjustable tongue in latches incorporating both push-pull and turn modes of operation without simultaneously describing them in simple push-pull latches and in simple turn latches.

[0035] Further advantages of the adjustable tongue are described in connection with the catches.

[0036] All embodiments of the present invention described incorporate the adjustable tongue whether this is specifically stated in the description or not.

[0037] Figure 2 is a front elevation of the tongue 2 and tongue carriage 5. The tongue carriage 5 is designed so as to enable push-pull latch operation together with the conventional turn latch operation.

[0038] The rear of the tongue carriage 5 is provided with a recess 12 which accommodates the handle shaft 1 when the tongue and tongue carriage are retracted. The top and bottom of the rear portion of the tongue carriage 5 are both provided with respective wall projections 13. The wall projections 13 stand-up from the tongue carriage 5 and the forward ends thereof project for a short distance perpendicularly from the top and bottom sides of the tongue carriage 5. These lateral projections engage respective springs which act against the casing of the latch so as to bias the tongue carriage 5 and tongue 2 into the projecting position. The portion of the walls 13 coincident with the top and bottom edges of the tongue carriage 5 serve to confine the biassing springs. The rearward ends of the walls 13 are acted upon by the conventional D-lever arrangement so as to retract the tongue carriage 5 with the conventional turn latch operation. The height of the walls 13 is such that the tongue carriage is retained within the latch casing so as to be freely movable backwards and forwards but not across the width of the latch.

[0039] An aperture 14 is provided where the crank arm engaging formation 10 has been "struck-up" and this aperture is extended towards the front of the tongue carriage 5. The aperture 14 enables the tongue carriage 5 to be guided by a cylindrical socket (figure 12) which acts as a stop for movement of the tongue carriage 5 and which is also used for coupling together the two case plates of the latch.. The apertures 15 are also provided to enable the tongue carriage 5 to slide without restriction by further case fixing bolts. The lug 16 is provided to cooperate with a catch which will be described later. The tongue 2 may be circular in cross-section and this variation from the conventional tongue profile is permitted by the provision of the catch arrangement which is to be described. The aperture 14 permits crank arm 8 to engage formation 10 when the shaft assembly bracket 4 is attached to a case plate of the latch.

[0040] Figures 3A and 3B show one of the case plates of the latch casing and the casing end plate which is attached thereto. Figure 3B is a section on the line A-A of Figure 3A. The case plate 17 has two struck-up lugs 18 which act as abutments for the springs which act upon the walls 13 of the tongue carriage 5 to bias the tongue 2 into its projecting position. A boss 19 is provided for the D-lever of the conventional turn latch arrangement. Aperture 20 is provided so as to enable the crank arm 8 to enter the casing and engage the formation 10 of the tongue carriage 5. The shaft assembly bracket 4 is secured to the outside of the casing plate 17 and it will therefore be appreciated that the latch assembly is independent of door thickness. Variations in door thicknesses are accommodated by different length handle shafts 1 or by variation of handle attachment. The end plate 21 of the latch casing is provided with a circular aperture 22 for the tongue 2 and is also provided with a circular aperture 23 for a catch pin (Figure 12). The case plate 17 is provided with a lug 24 which acts as a support for a catch pin holder.

[0041] The end wall of the case plate 17 is provided with a threaded aperture 25 for engagement with a catch cylinder shaft screw.

[0042] Figure 4 shows the other case plate 26 of the latch casing. The case plate 26 is provided with two walls 27 which confine the upper spring acting on the tongue carriage 5. These are necessary since the latch casing is extended at the top to accommodate the catch arrangement. The lower spring acting on the tongue carriage 5 is confined by the side walls of the case plates 17 and 26. The case plate 26 is provided with lugs 18 which correspond with the lugs 18 on the case plate 17 so as to provide a surface against which the tongue carrige biassing springs act.

[0043] The case plate 26 is also provided with a port 20 to allow access of the crank arm 8 should the shaft assembly bracket 4 be secured to the case plate 26 instead of the case plate 17. This is necessary if the latch assembly is to be ambidexterious, that is so that the latch unit can be situated on either the left-hand or right-hand side of the door.

[0044] Reference numeral 28 indicates a cylindrical socket which is threaded to accept a screw which holds the case plate 17 and 26 together. The cylindrical socket 28 also acts as a guide for the tongue carriage 5 and as a movement limiting stop as described above. The wall 29 of the case plate 26 is a combined stop and guide for the catch pin assembly. Wall 30 of case plate 26 is also a support for the catch pin.

[0045] Figures 5A, 5B, 5C and 5D show details of the shaft assembly bracket 4 and figures 5A and 5B also show the crank 3 in position on the bracket 4. The shaft assembly bracket is secured to one of the case plates.

[0046] The shaft assembly bracket 4 is responsible for a number of functions in respect of both the push-pull and the turn latch modes of operation. The shaft assembly bracket 4 has a back plate 31 with a central aperture 32 through which the handle shaft 1 passes. The back plate 31 has a horizontal bracket 33 at its forward edge on which is provided a vertical shaft 34 which is the pivot for the crank 3. An adjacent recess 35 in the back plate 31 allows for rotation of the crank arm 8. The back plate 31 has an angle bracket 36 which projects perpendicularly with one side acting as a base support and the other side acting as a vertical wall. Two further vertical walls 37 are provided on the base support 36. These walls 37 are spaced apart from the base plate 31 and project beyond the edge of the base support 36 parallel to the vertical wall 36. The walls 37 support a bearing plate 11 which is parallel with the base plate 31. The bearing plate 11 is circular and has a central aperture to enable the handle shaft 1 to pass therethrough.

[0047] The bearing plate 11 has a small slot 39 in its circumference which is used to retain one end of the handle shaft biassing spring 6. The other end of the spring 6 is retained in a hole 40 in the handle shaft 1 (figure 1).

[0048] The inner face of the bearing plate 11 acts as a stop for limiting longitudinal displacement of the handle shaft 1. The base plate 31 of shaft assembly bracket 4 is provided with two threaded apertures 41 which are used to secure the bracket 4 to the case plate 17 or 26. Two further apertures 42 are provided in the base plate 31 and these match corresponding apertures in the case plates 17 and 26 and are provided to accommodate fixing screws.

[0049] Figures 5C and 5D show vertical sectional elevations taken along the line A-A in figure 5A. Figures 5C and 5D show alternative configurations of the walls 37. The profile of the walls 37 controls the turn latch mode of operation. The implication of the alternative profiles of the walls 37 are explained in combination with the cross-section of the handle shaft 1 shown in figure 6.

[0050] It can be seen from figures 5A and 5B that crank arm 7 has a vertical downwardly extending peg at the free end thereof.

[0051] The peg 43 is engaged by the formation 9 of the handle shaft 1 and this arrangement is also discussed in more detail together with the profile of the handle shaft 1 shown in figure 6. Figure 6A-is a plan view of the handle shaft 1. Figures 6B, 6C, 6D, 6E & 6F show the cross-sectional profile of the handle shaft 1 taken on the lines designated by the respective letters, e.g. figure 6B is taken on line B-B. The central portion 44 of the shaft 1 is of square cross section as shown in figure 6B. The D-lever of a conventional latch seats on portion 44 and the square section of that portion insures that the D-lever is rotated with the handle shaft 1. For most of its length the handle shaft 1 is of circular cross section as shown in figure 6C. The extreme ends 45 of the shaft 1 are of reduced squared cross-section and are shown in figure 6D. These portions 45 are engaged by handles (not shown), the square cross-section enabling the handles to rotate the shaft 1. The shaft 1 is able to slide through the D-lever.

[0052] The formation 9 of the handle shaft 1 which is engaged by the crank arm 7 has a cross-section shown in figure 6E. When the latch is assembled the formation 9 is retained within the shaft assembly bracket 4. Abutment between the formation 9 and bearing plate 11 of bracket 4 limits movement in one londituninal direction of the shaft 1. The formation 9 comprises two spaced apart walls which are each in the shape of a sector of a respective annul as which surrounds the shaft 1. The peg 43 of crank arm 7 is located between the walls of formation 9 so that the free end of the arm 7 must follow longitudinal movement of the shaft 1. The diameter of the peg 43 is somewhat smaller than the separation between the two spaced apart walls 9. However, the peg 43 and hence crank 3 are not affected by purely rotational movement of the handle shaft 1.

[0053] The biassing spring 6 which is retained by hole 40 of the handle shaft 1 and by the slot 39 bearing plate 11 of shaft assembly bracket 4 also biasses the handle shaft 1 to a rotational position of rest. In this position of rest the formation 9 is located as indicated by figure 6E.

[0054] The walls of the formation 9 extend for 116" around the circumference of the shaft 1. Consequently, when the walls 37 of shaft assembly bracket have the profile shown in figure 5C, the handle shaft 1 can be rotated through 32% in either direction before the formation 9 abuts against one of the respective walls 37.

[0055] When the handle shaft 1 is rotated the D_-lever, shown in front elevation in figure 7A and in plan elevation in figure 7B, is rotated due to the action of the square section portion 44 of the shaft 1. The D-lever 46 acts on one of the walls 13 of the tongue carriage 5 and thereby retracts the tongue 2. Due to the symmetry of the D-lever and the walls 13, the tongue 2 is retracted irrespective of direction of rotation of the shaft 1.

[0056] The shaft 1 could possibly be returned to its rotational rest position by the springs acting on the tongue carriage 5. However, this would necessitate the use of relatively powerful springs and use of the spring 6 as described above is considered preferable.

[0057] The alternative profile of the walls 37 of shaft assembly bracket 4 illustrated in figure 5D provide an either-or effect. The reason for this alternative is that if a person wishes to open the door using the conventional turn mode then there maybe sufficent resistence to the opening of the door, for example, a closure spring maybe fitted to the door, to overcome the force of spring 6 so that the handle shaft 1 is displaced longitudinally. This could prove to be very disconcerting if such movement of the door handle is unexpected. The arrangement of figure 5D ensures that if the handle shaft 1 is rotated it cannot be pulled against the action of spring 6 and if alternatively the shaft 1 is pulled against the action of spring 6, then the shaft 1 cannot be rotated. The sharpness of the either-or effect can be modified by altering the profile of the walls 37. The actual choice would be a matter of user preference.

[0058] Rotation of the handle shaft 1 from its rest position will cause one end of the formations 9 to abut the surface 47 of the wall 37. Consequently, the step portion 48 will prevent the shaft 1 from being withdrawn against the action of the spring 6. Alternatively, if the handle shaft 1 is withdrawn from its rest position against the action of the spring 6 then the formation 9 will, loosely, abut against the top surface of the step portion 48. It will not subsequently be possible to rotate the handle shaft 1 while it is in the withdrawn position.

[0059] Figure 6A and 6F show the provision of a key 49 in the handle shaft 1. The key 49 acts to prevent the shaft 1 being pushed inwards from its rest position, when operated from the pull to open side of the door. When the latch is assembled the key 49 is virtually in contact with a side face 50 of the D-lever 46. If the shaft 1 is rotated, the key 49 and the D-lever 46 will rotate together. No extra anti-rotational friction is created even if the shaft 1 is being urged inwards as well as being rotated. Such extra friction would arise if the key 49 bore into a non-rotating part.

[0060] In the above description several references have been made to features associated with a catch. One example of this feature of the invention will now be described.

[0061] With a conventional turn latch the tongue projects while the door stands open. On closing the door the handle can be rotated so as to withdraw the tongue, thereby avoiding the tongue striking against the door post. When the door is fully closed the handle is released and the tongue springs into a recess so as to latch the door. If one considers a simple push-pull latch then it will be apparent that there is minimal resistence as the door is pushed towards the closed position. The handle will not be able to exert a sufficent force to change the state of the latch mechanism and withdraw the tongue 2. Consequently, the tongue 2 will remain in its projecting position and will strike against the door post.

[0062] It has been explained above how this nuisance may be considerably mitigated by the introduction of the adjustable tongue. But it is also possible to eliminate the nuisance entirely as will now be explained.

[0063] The present invention provides a catch which retains the tongue in the retracted position as the door is opened. The tongue will therefore not strike against the door post when the door is closed again, and the nuisance referred to will be avoided. This arrangement will also have the advantage that it reduces the risk of articles, such as people's clothing, being caught by the latch tongue while the door is open.

[0064] It is not necessary or desirable for the catch to release the tongue until the door is fully closed. 'When the door is fully closed the problem of lack of resistence to movement of the door upon pushing or pulling the handle is absent. Operation of the handle can therefore be used to release the catch so that the tongue projects into the door post recess, when the door is fully closed. However, this form of operation may be considered inconvenient and if the open door is closed by a gust of wind the door will not latch and will be free to strike repeatedly against the door post. Consequently, the illustrated embodiments of the invention include automatic catch release mechanisms so that the door is automatically latched when closed.

[0065] Figure 8A shows a catch pin 51. Figures 8B and 8C are plan and front elevations respectively of a pin holder 52. The pin 51 is cylindrical, domed at one end and threaded at the other. The threaded end of the pin 51 engages the threaded block 53 of the pin holder 52. The block 53 has an external width ensuring a sliding fit of the pin holder between the case plates of the latch. As can be seen from figures 8B and 8D a cut out 54 is provided in the holder 52 at the rear of the threaded aperture of the block 53. This increases the adjustment available for the overall length of the pin 51 and pin holder 52. The ability to adjust the projecting length of the pin 51 is required in order to match any adjustments made to the projecting length of the tongue 2, as described above. To the rear of the block 53, the pin holder 52 has a L-shape cross section and the side wall 55 of that cross section strengthens the pin holder. Such strengthening is provided since the plan surface of the pin holder 52 has a cut out section 56 which is sawtooth in shape with a perpendicular edge and an inclined edge, the inclined edge being closest to the block 53. From the apex of the sawtooth to the base thereof, the inclined surface has a gradient of 2:3. The pin holder 52 is terminated by a flat tail 57 which is of reduced width. The purpose of the tail 57 is to provide support for the pin holder 52 and this is shown in Figure 8E where the tail 57 can be seen to be supported and guided by the case plates 17 and 26.

[0066] Figures 9A, 9B and 9C show front, end and plan elevations respectively of the catch cylinder 58. The catch cylinder 58 is hollow and is provided with two arms 59 and 60 which project perpendicularly from its external surface. The arm 60 is located adjacent the front end of the cylinder and extends downwardly while the arm 59 is located adjacent the rear of the cylinder and extends upwardly. The arms 59 and 60 lay in substantially the same plane and both are of rectangular cross section. The cross section of the arm 60 is aligned with the longitudinal axis and the ends of the cylinder 58. The cross section of the arm 59 is, however, inclined with respect of the longitudinal axis of the cylinder 58. Its angle of inclination has a gradient of 2:3 and this is the same as the gradient of the inclined surface of cut-out 56 of pin holder 52. The catch cylinder 58 is a sliding fit on the catch shaft 61 shown in figure 90. The catch shaft 61 has an enlarged head at one end which acts as a stop for cylinder 58 and the other end of the shaft 61 is threaded and engages aperture 25 in case plate 17 (figure 3B). The operational relationship between the pin 51, pin holder 52, catch cylinder 58 and tongue carriage 5 are shown in figures 10A, 10B, 10C and 11A, 11B, 11C.

[0067] Figure 10A shows a partial front elevation of the catch cylinder and pin holder mounted within the latch casing. When the catch shaft 61 is secured to the case plate 17 the catch cylinder 58 is parallel to the pin and pin holder and adjacent thereto such that the arm 59 extends through cut out 56. The arm 59 rests against the inclined surface of the pin holder 52 provided by cut-out 56.

[0068] A spring acts between the projections 24 and 30 and the shoulder of the pin holder 52 presented by the reduced width of the tail 57 of the pin holder. A twist spring seats on the enlarged end of the catch shaft 61 and acts upon the cylinder 58 so that the arms 59 and 60 are urged in an anti-clockwise direction as viewed from the end plate of the latch. The springs are ommitted in figures 10 and 11.

[0069] The arm 59 of the catch is urged against the inclined edge of the pin holder 52 by the twist spring provided on shaft 61. Consequently, as the pin 51 moves in or out, the catch cylinder 58 is caused to rotate and the lower catch arm 60 moves in a plane parallel to the end plate 21 of the latch.

[0070] When the door is closed the pin 51 is retracted, by the action of a guard plate provided on the door post. As shown by figures 10A and 10B the retraction of pin holder 52 causes the arm 59 to be displaced by the inclined surface 56 of the pin holder. This results in the catch cylinder 58 being rotated in a clockwise direction as viewed from the end plate of the latch and the arms 59 and 60 are displaced from the vertical plane. As shown by figures 10A and 10C the arm 60 of the catch cylinder 58 does not obstruct the lug 16 of the tongue carriage 5, and the tongue carriage 5 is therefore pushed forward by the biassing springs. In this position the tongue 2 is in its projecting position and the door is latched.

[0071] When the door is to be opened the tongue 2 and tongue carriage 5 are withdrawn either by turning or pulling the handle so as to unlatch the door. As the door opens the pin 51 is urged into a fully projecting position by the spring acting against case plate projections 24 and 30. The inclined surface 56 of the pin holder 52 moves past the arm 59 of catch cylinder 58 so that when the pin 51 is fully projecting that is block 53 abuts end plate 21, the arms 59 and 60 of the catch cylinder 58 have once again returned to the vertical plane. This position is illustrated in figures 11A, 11B and 11C. It can be seen that the lower arm 60 of the catch cylinder 58 passes in front of the lug 16 of the tongue carriage 5 so that when the operator releases the handle of the door latch the lug 16 abuts against the arm 60. This prevents the tongue carriage 5 from moving forward thereby retaining the tongue 2 in its retracted position as long as the door remains open.

[0072] It is now convenient to consider the advantagages offered by the adjustable tongue 2 in connection with the catch. Using the push-pull mode of operation to open the door causes the crank 3 to rotate which in turn retracts the tongue carriage 5. As one progressively pulls the handle, the tongue 2 is progressively retracted until the tongue 2 is just withdrawn from the retaining recess. The door will now start to swing open and consequently there is a significant reduction in the reaction against the pulling force exerted on the handle. Therefore the tongue 2 will not be retracted any further into the door by the pull on the handle once the door has started to swing open. Indeed, the tongue 2 will be pushed out by the springs which act on the tongue carriage 5. The tongue 2 will therefore be urged against the guard plate, which is to be described, on the door post as the door opens, except in so far as the tongue 2 is prevented from doing so by subsequent action of the catch.

[0073] The catch therefore needs to be able to operate while the tongue 2 is resting on the guard plate. Consequently, it is necessary for the lug 16 to be behind the arm 60 of the catch when the tongue 2 is in this position. If this were not so, the catch would not be able to operate when the door is opened by pulling the handle since the lug 16 would not be drawn behind the arm 60. The situation is somewhat different when the door is being opened by turning the handle since retraction of the tongue carriage 5 can continue past the position where the tongue 2 is just withdrawn from the retaining recess.

[0074] In practical terms, it is not only necessary for the lug 16 to be behind the catch when the door is opened by pulling on the handle, but the lug 16 should not be too far behind the arm 60 of the catch. The distance by which the lug 16 is behind the arm 60 of the catch represents the amount of back-lash that will occur. When the door is standing open the tongue carriage 5 will be urged forward by the springs so that the lug 16 bears against the catch, and it is this configuration which determines how far the tongue 2 projects. For example, if the lug was 3 millimetres behind the catch when the catch commenced operation, the tongue 2 would project 3 millimetres further than necessary when the door is standing open. This could mean that it is correspondingly more difficult to prevent the tongue 2 from striking the door post when subsequently closing the door. It is preferred that the lug 16 is retracted upon opening the door, sufficiently to allow the catch to operate but with minimal excess retraction of the lug 16 behind the arm 60 of the catch.

[0075] An investigation of a number of doors indicates that the clearance between the door and the door post will often vary in the range from 1 millimetre to 7 millimetres. The provision of an adjustable tongue deals with the problem of such a large variation in clearances. By making the effective length of the tongue 2 adjustable it becomes possible to ensure that the lug 16 is always retracted to the same position with respect to the arm 60 of the catch when the tongue 2 just becomes clear of the retaining recess, irrespective of the clearance between the door and the door post. The adjustable tongue 2 is used so as to take up the variation in clearance between the door and door post when the latch is first installed. If, after the latch has been correctly installed the dimensions of the door alter due to variations in humidity, then such variations can be compensated for by adjusting the tongue. However, in the majority of applications it is expected that humidity variation would not require adjustment of the tongue on a regular basis.

[0076] The tongue is adjusted to ensure the correct operation of the catch. However, as has already been explained, in order to achieve a smooth and easy action when opening the door by pulling the handle it is necessary that the tongue should not overlap the guard plate by more than a comparatively small amount.

[0077] This is aslo arranged by adjusting the tongue and it is necessary to show that the two adjustments may be reconciled; that is to say that a single adjusted position of the tongue will satisfy both the requirements.

[0078] The two adjustments can be reconciled by correct dimensional design of the latch and the catch. Fig. 10A shows the tongue in the projecting position, and Fig 11A shows it in the retracted position with the lug 16 behind the arm 60 of the catch. It will be seen that a single adjusted position of the tongue will satisfy both the requirements provided it is only necessary for the tongue carriage 5 to be retracted by a comparatively small distance between the first state and the second. This may be achieved by correct dimensional design.

[0079] Figure 12 is a vertical sectional view taken along the centre of the fully assembled first embodiment of the invention. The latch is shown as it would be if the door was standing open. The catch pin is in a projecting position and the tongue is retracted. The springs acting on the catch mechanism are shown. The guard plate for the door post required by this first embodiment of the invention is illustrated in the figures 13A and 13B.

[0080] The guard plate 62 has an aperture 63 through which the tongue 2 passes when the door is closed. The aperture 63 could be circular but sufficient tolerance must be provided to account for any inaccuracies or changes in alignment of the latch mechanism and guard plate. An inclined ramp 64 is provided for the catch pin 51 and it is the action of the catch pin 51 on the ramp 64 which causes the catch to release the tongue when the door is closed. The configuration of ramp 64 must control the release of the catch so that the tongue 2 is released as the door reaches the fully closed position. However, a ramp 65 is provided.adjacent the aperture 63 so that the tongue 2 will be retracted as it passes up the ramp 65 should the tongue 2 be in the projecting position as the door closes due to, for example, the catch mechanism being accidently released when the door is open. The relative configuration between the ramps 64 and 65 is illustrated in figure 13B. The catch cannot hold the tongue 2 precisely in the position at which the tongue clears the retaining recess and when the door is standing open the tongue 2 will have moved forward fractionally from this position. Therefore, if the guard plate were flat, the tongue 2 would strike the guard plate upon closure of the door. The ramp 65 is provided to mitigate such strike.

[0081] Indeed, a simple latch may be constructed which does not include the provision of a catch. The tongue 2 would be pressed out by the springs, acting on the tongue carriage 5, while the door is standing open and the tongue would strike the guard plate 62 open closure of the door. When the door is pushed fully closed, the tongue 2 would be urged into the retaining recess by the springs. In a simple latch of this type the provision of an adjustable tongue and the provision of a sloping ramp 65 on the guard plate 62 would both act to mitigate strike of the tongue 2 on the guard plate 62 when closing the door.

[0082] The action of the catch pin 51_f on the ramp 64 also causes the lower catch arm 60 to rotate to a vertical position in front of the lug 16 when the door is opened. It is necessary for the lug 16 to have been withdrawn behind the plane of movement of the lower catch arm 60 when the arm 60 moves towards the vertical position. The ability to adjust the lengths of projection of the tongue 2 and catch pin 51, together with the relative configurations of the ramps 64 and 65, ensure that the desired relative positions of the lug 16 and catch arm 60 may be attained irrespective of the clearance distance between door and door post.

[0083] When the guard plate 62 is fitted, grooves must be cut into the door post therefore this type of latch is inconvenient to install if the door post is formed of a material such a aluminium rather than a material such as wood.

[0084] In an alternative embodiment the motive power for the catch is obtained not from a pin travelling across a guard plate, but from a stud fixed to or acting on the rebate of the door post.

[0085] The stud acts on a vane projecting from a catch cylinder which is biased by a twist spring. The middle portion of the catch cylinder is provided with a spiral akin to that of a corkscrew. Retention of the tongue in the retracted position is achieved by cooperation of the spiral with a lug on the tongue carriage. Operation of the catch is achieved by the twist spring rotating the catch cylinder and the spiral pressing on the tongue carriage lug as the door is opened.

[0086] A modification of the above described catch involves the provision of a catch pin which projects from the latch in a similar fashion to the first described catch. However, the pin is secured to the free end of the vane of the above described catch. The catch cylinder is rotated not by a stud acting on the vane but by the catch pin cooperating with a guard plate designed to suitably control movement of the pin.

[0087] The described catches retain the tongue in the retracted position mainly to avoid strike caused by the tongue being biased into its projecting position. An alternative is to eliminate the bias and to arrange projection of the tongue upon closure of the door by means of a tongue moving mechanism. The arrangement can be similar to the second of the described catches. An internally threaded hollow barrel is provided on the tongue carriage and the catch cylinder comprises a meshing externally threaded barrel. The catch cylinder is rotated by action on the vane and rotation is transmitted to the catch cylinder threaded barrel via by a relatively strong twist spring. Such transmission by the twist spring enables storage of rotational energy during various stages of operation of the catch. Relatively small rotation of the catch cylinder is transferred into a rotation of the catch barrel sufficiently large to retract the tongue by the necessary distance by use of a suitable pitch of the barrel threads; action with the tongue carriage barrel resulting in linear movement of the tongue.

[0088] The above described embodiments of the invention are based upon or incorporate the method of converting a pushing or pulling action on the handle shaft to retract the tongue carriage using the crank 3 as illustrated in figures 1A and 1B. An alternative arrangement which avoids use of the crank will be described with reference to Figure 14. Figure 14 shows a handle shaft 1 which is of circular cross-section apart from a central portion 44 which is of square cross-section. Shaft 1 has a respective recess 66 formed near each end. Each recess 66 is partially defined by an edge 67 having the configuration of a slow spiral. The shaft 1 is used in place of the shaft of a conventional mortice latch which employs a D-lever of the type illustrated in figure 7A. Shaft 1 is prevented from moving longitudinally through the D-lever once the components have been fitted together. The precise mechanism for achieving this is not important and is considered to be within the grasp of a person skilled in the art.

[0089] This embodiment of the invention_requires specially designed door handles. The handles (not shown) are designed such that they can move longitudinally on the shaft and can also rotate about the shaft. Each handle has an internal lug, part of which is illustrated by reference numeral 68 in figure 14. Lug 68 extends into recess 66 and bears against the spiral shaped edge 67. The handle is constrained, advantageously by the handle trim, such that the lug 68 may be turned in one direction, corresponding to left of line AB in figure 14, but not, from the rest position, in the opposite direction.

[0090] The handle associated with the lug 68 shown in figure 14 will be able to turn in an anticlockwise direction. The lug 68 acts on edge 67 and the shaft 1 will rotate in the anticlockwise direction with the handle. As the shaft rotates the D-lever acts to retract the tongue carriage. When the handle is released the tongue carriage, D-lever, shaft and handle are returned to their starting positions by biasing acting on the tounge carriage and/or by supplementary biasing.

[0091] An alternative mode of operation is effected by pulling the handle. Lug 68 acts on spiral edge 67 and since the handle is restrained from the turning in a clockwise direction, the shaft 1 is forced to rotate in an anticlockwise direction.

[0092] Movement of the tongue carriage and return to the starting position is as. described above.

[0093] Since the handle may only be turned in one direction it may be preferable for the handle to be L-shaped rather than circular. In figure 14 the illustrated lug 68 is associated with the pull-to-open end of the shaft to be situated on the righthand side of the door. If the pull-to-open end of the shaft were situated on the left side of the door the spiral of edge 67 would need to be in the opposite direction to that indicated. Differently machined shafts could be provided for these two eventualities. However, it may also be possible to make two opposite recesses on opposite sides of one shaft. Inverting the shaft would then enable the latch to be transferred from the right to the left side of the door.

[0094] A further arrangement for translating movement of the handle shaft into movement of the tongue carriage is illustrated with reference to Figure 15. Figure 15 is a simplified sketch and is only intended for illustration of the concept of this alternative arrangement. The handle shaft 1 can be rotated by rotation of a handle or can move longitudinally as a result of a push or pull action being applied to a handle. A bowl shaped recess 69 is provided in the upper surface of the shaft 1. A crank mechanism 70 is used in place of the conventional D-lever.

[0095] Crank mechanism 70 pivots about an axis 71 parallel with the shaft 1 but offset therefrom. Mechanism 70 comprises two arms, 72 and 73, which extend perpendicularly with respect to axis 71. Arm 72 abuts against the tongue carriage and arm 73 carries a pin 74 at its free end. The pin 74 rests in bowl 69. In the rest position pin 74 sits at the centre of the bowl 69 and the tongue protrudes from the edge of the door. If handle shaft 1 is rotated or moved longitudinally, pin 74 rides up the side of the bowl 69. This results in movement of arm 73 causing mechanism 70 to pivot and arm 72 to act on the tongue carriage so as to retract the tongue.

[0096] Another embodiment of the handle shaft-to-tongue carriage mechanism is a modification of the arrangement shown in Figures 1A and 1B. In this embodiment the D-lever can be omitted while retaining both rotation and push-pull modes of operation. The segments 9, which are most clearly illustrated in Figure 6A, are modified as shown in Figure 16. The segments 9 are formed into a bow shape. Pin 43 is moved backwards as a result of either pulling or rotating the shaft.

[0097] Embodiments have been described in which various permutations of a crank arrangement have been used for transferring motion from the handle shaft to the tongue carriage.

[0098] An alternative will now be described.

[0099] Figure 17 illustrates the means whereby the latch is opened by pushing or pulling a handle, in this alternative arrangement.

[0100] Shaft 75 extends transversly through the latch body. It will be appreciated that in normal use when the latch is fixed in a door shaft 75 will also extend through the thickness of the door. Fin 76 is attached to the central portion of the shaft 75 on the side of shaft 75 which lies furthest from the tongue 77 when shaft 75 is in its normal rest position. 'Handles (not shown) are attached to the ends of shaft 75 on both sides of the door. Shaft 75 may be moved longitudinally by pushing or pulling the handles depending upon which side of the door the latch is being operated from, but in either case the longitudinal motion will be in the same direction. When shaft 75 is moved longitudinally the edge 78 of fin 76 will press against the edge of plate 79 attached to tongue carriage 80, thus causing tongue carriage 80 to move back against the pressure of springs. Tongue 77 will be retracted thus unlatching the door.

[0101] Figure 18 further illustrate the longitudinal motion of the shaft 75. Shaft assembly bracket 81 is attached to the outer face of one of the latch body plates (not shown)..The circular portion of shaft 75 slides through a circular hole in a bush 82 attached to shaft assembly bracket 81. Figure 18 shows the shaft 75 in its normal rest position, and it will be observed that there is an interval between the outer face of segment 83 fixed to shaft 75 and the inner face of bush 82. The outward longitudinal movement of shaft 75 is limited as the outer surface of segment 83 comes into contact with the inner surface of bush 82.

[0102] It can be seen from Figure 17 that the tongue 77 is threadedly engaged with tongue carriage 80. This enables the extent to which the tongue 77 protrudes from the door to be varied. The provision of an adjustable tongue is considered to be an important feature of the latch particularly in connection with push-pull operation, as will now be explained.

[0103] Suppose the door is standing shut and latched with the tongue protruding into the hole in the door post, and suppose that a person wishes to open the door by pulling the handle. Pulling the handle will tend to move the shaft 75 longitudinally and cause the tongue 77 to be retracted as has been explained. However part of the force of pulling on the handle will also be transmitted to the door and tend to swing it open. If tongue 77 is not fully retracted from the hole in the door post this movement of the door will have the effect of pressing the tongue against the edge of the hole in the door post. This will cause friction which will tend to oppose the retraction of the tongue. The problem is thus worsened. Because of the increased friction one needs to pull harder on the handle, which causes increased friction. This problem can be satisfactorily avoided by reducing the extent of projection of the tongue to a minimum. If the tongue protrudes deeply into the hole in the door post this frictional effect may be severe and cause considerable difficulty in opening the door by pulling the handle. It is therefore desirable that the distance which the tongue overlaps with the hole in the door post be kept to the minimum consistent with the need to keep the door securely latched.

[0104] It will furthermore be understood that the gap between door and door post is not the same in every instance. It is therefore desirable to be able to adjust the amount by which the tongue protrudes so as to meet the requirement in each instance.

[0105] Figure 19 illustrates the means whereby the latch is opened by turning the handles, and this is not different in principal from conventional latches alreadly in use.

[0106] The squared central portion of shaft 75 passes through the square hole in the D-lever 84. When the shaft is rotated by turning the handles the rotation of the shaft 75 causes the D-lever 84 to rotate. This will exert a force on one of the lugs 85 attached to the tongue carriage 80 thus forcing the tongue carriage 80 backwards against the pressure of the springs 86 to retract the tongue 77 and unlatch the door.

[0107] The shaft 75 is returned to its rest position, after either rotational or push-pull operation, by the return action of the tongue carriage 80, i.e. by action of springs 86. A further return spring may optionally be added as in the case of the embodiment of Figure 1. It is believed to be preferable for the rear edge 78 of fin 76 to be curved in order to assist the smooth return of shaft 75 to its rest position.

[0108] Inward movement of shaft 75 is limited by a lug on the shaft and arrangements for the mode selector mechanism, fixing and ambidexterity are the same as described for the embodiment of Figure 1.

[0109] Details of the described embodiments may be varied without departing from the scope of the invention. The embodiments may be modified to emulate latches designed for specific purposes. For example, one common existing type of latch is constructed so that rotation of the handle on one side of the door does not cause the handle on the other side to rotate. In this type of latch there are two separate hollow shafts, one on each side of the door. A separate D-lever is attached to each shaft, and each D-lever retracts the tongue carriage independently of the other. It will be seen that the mechanisms described herein could easily be adapted by duplication or other means to operate in a similar way.

[0110] There is also a common existing type of latch in which the tongue is detachable from the body of the latch and the tongue carriage. Latches of this type commonly have a cylindrical body which is located in a hole drilled through the thickness of the door. The separate case for the tongue is located in a hole drilled from the edge of the door, and joined by appropriate fastenings to the latch body and tongue carriage. It will be seen that the mechanisms described herein could easily be adapted to a similar form.

[0111] Several of the described embodiments are relatively sophisticated. Some of the simple embodiments have been found to be practical.

[0112] In particular, encouraging tests have been conducted with a simple latch in which the tongue may be retracted by turning the handle or by pushing or pulling the handle. This latch has an adjustable tongue with a steep chamfer at its tip and does not have a catch or turn/push-pull selector. The shaft return spring is also omitted since it is found that the shaft will return to its longitudinal and rotational rest position under the influence of the tongue carriage springs alone. The latch does not look or feel odd in comparison with a conventional latch. Use of the latch can be easier and less clumsy than a conventional latch. Manufacture is not significantly more difficult than conventional latches and installation is the same except for the small additional task of adjusting the tongue. The latch need not be less reliable or less robust than its conventional counterparts

[0113] During trials the tongue was adjusted so as to project approximately 3 mm into the guard plate recess. Opening the door using either mode of operation, rotation or push-pull, required only minimum movement of the handle and yet the door remained latched even if subjected to moderate force winds or the like. The dual mode of operation and omission of the selector mecanism enabled the door to be opened by applying only a small and undefined force to the handle.

[0114] When closing a door fitted with a conventional latch it is usual to turn the handle to partially retract the tongue in order to minimise strike of the tongue with the guard plate. Using the adjustable tongue the latch will already be in the optimum condition for minimum strike while closing the door.

[0115] Closing the door can be virtually noiseless and attention-free. Thus with the tongue correctly adjusted the latch need not suffer much disadvantage by omitting the catches described in some of the embodiments.

[0116] There have now been described a number of embodiments of the present invention. It will be readily appreciated that many modifications can be made to the detail of the described embodiments and to the arrangement of the embodiments of the fundamental push-pull type latch.

Claims

1. A door latch comprising a tongue (2) having a projecting position for latching a door, a handle shaft (1) having a longitudinal axis, at least one handle which acts on the handle shaft (1) characterised by means (3, 5, 46) for transmitting motion of the shaft (1) to the tongue (2), whereby the tongue (2) can be retracted from its projecting position to unlatch the door in at least two modes including moving the handle along the said axis, and by rotating the handle with respect to the said axis.

2. A door latch as claimed in claim 1, characterised in that the handle is attached to the handle shaft (1) such that rotation of the handle causes rotation of the handle shaft (1) and movement of the handle along the said axis causes movement of the handle shaft (1) along the said axis.

3. A door latch as claimed in claim 2, characterised in that the means (3, 5, 46) for transmitting.motion of the shaft (1) to the tongue (2) comprises a crank (3) having two arms (7,8) projecting from a spindle which is pivoted about a fixed axis, one arm (7) being acted upon by the handle shaft (1) and the other arm (8) acting on a formation (5) attached to the tongue (2).

4. A door latch as claimed in claim 2, characterised in that the means (76-84) for transmitting motion of the shaft (1) to the tongue (2) comprises a surface (78) inclined with respect to the said axis and a member (79, 80) attached to the tongue (2), longitudinal movement of the handle shaft (1) resulting in movement of the member (78, 80) by the inclined surface (78) to thereby retract the tongue (2).

5. A door latch as claimed in claim 3 or 4, characterised in that the means (3, 5, 46) for transmitting motion of the shaft (1) to the tongue (2) also includes a D-lever (46) for transmitting rotational movement of the shaft (1) to the tongue (2).

6. A door latch as claimed in any of claims 2 to 5, characterised in that the means for transmitting motion of the shaft (1) to the tongue (2) includes selector means (9, 37) which prevent the handle shaft (1) moving along its longitudinal axis while the handle shaft (1) is being rotated to unlatch the door and vice versa.

7. A door latch as claimed in any preceding claim, characterised in that the latch comprises a catch (51-60) which retains the tongue (2) in a retracted position when the door is opened.

8. A door latch as claimed in any preceding claim, characterised in that the extent to which the tongue (2) projects from the body (26) of the latch when in the projecting position is variable.

9. A door latch as claimed in claim 6, characterised in that the selector means (9, 37) comprises a collar (9) which is attached to and partially encircles the handle shaft (1) and a pair of guides (37) parallel with the longitudinal axis of the handle shaft (1), the collar (9) and guides (37) being arranged such that rotation of the handle shaft (1) positions the collar (9) adjacent the end of at least one guide (37) thereby preventing simultaneous push, or pull, operation of the latch and such that pushing or pulling the handle shaft (1) causes the collar (9) to move along the guides (37) against which the collar (9) abuts to prevent simultaneous latch operation by rotation of the handle shaft (1).

10. A door latch as claimed in claim 7, characterised in that the catch (51-60) is operated by a catch pin (51) which projects from the latch and which is of adjustable operative length.

11. A door latch as claimed in claim 7, characterised in that the catch (51-60) comprises a catch cylinder having an external configuration which, upon rotation of the catch cylinder propels a carriage (5) to which the tongue (2) is attached thereby controlling movement of the tongue (2).

12. A door latch as claimed in claim 1, characterised in that the tongue (2) is moved into its projecting position by a tongue moving mechanism comprising a rotatable vane actuated by a pin which co-operates with or is secured to a door post, and a thread carrying member which transfers rotary movement of the vane to cause linear movement of the tongue (2).

13. A door latch as claimed in any preceding claim. characterised in that the door latch is ambidextrous in that the latch can be fitted to a door regardless of which edge of the door carries the door hinges.

14. A door latch as claimed in claim 1, characterised in that rotational movement of the handle with respect to the said axis causes the shaft (1) to rotate about the said axis and movement of the handle along the said axis causes the shaft (1) to rotate about the said axis.

15. A door latch comprising a body (26) and a tongue (2) which projects from the body (26) into a projecting position for latching the door and which is retracted from the projecting position to unlatch the door, characterised in that the extent to which the tongue (2) projects from the body (26) when in the projecting position is variable.

16. A door latch comprising a body (26) and a tongue (2) which projects from the body (26) into a projecting position for latching the door and which is retracted from the projecting position to unlatch the door, the latch further comprising a handle shaft (1) having a longitudinal axis and at least one handle which acts on the handle shaft characterised by means (3, 5, 46) for transmitting motion of the shaft (1) to the tongue (2). whereby the tongue (2) is retracted from its projecting position to unlatch the door by moving the handle along the said axis and the extent to which the tongue (2) projects from the body (26) when in the projecting position is variable.

Drawing