Field of the Invention

This invention relates generally to door and window furniture and is concerned in particular with arrangements for providing a drive coupling between a handle and a latch unit.

Background Art

Lever handles are preferable to knobs from a functional point of view, and are the normal form of door handle in commercial premises. Knobs cannot be operated by any means other than hand rotation, and are thus more difficult to operate for persons with any kind of grip or strength disability of the hand. Lever handles are not, however, without disadvantages. A spring return must always be provided to prevent lever droop and to ensure a horizontal equilibrium position. The need for a housing for this spring, and the traditional incorporation in a lever handle of an axial socket to receive the drive spindle, have meant that the range of lever handle shapes, though often embodying good design, has been quite limited.

In the case of knob handles, it is also usual for the knob to carry a socket to engage the latch drive spindle, and this socket may be integral, cast in situ, or provided as a separate unit attached to the knob. For example, Australian patent 673544 shows an assembly in which the knob drives the spindle via an intermediate connector which receives the spindle and is itself received in a central opening in the knob.

With knob handles, the knob is conventionally rotatable in an escutcheon plate which is fixed to a mounting or fixing plate secured to the door panel or latch casing.

Various hidden fixings have been used or proposed for connecting the two plates, including threaded attachment at centre bosses, threaded engagement adjacent the rims, as described in the aforementioned patent 673544, the face-to-face bayonet fitting of

Australian patent 653083, and the lug and groove twist action of Australian patent application no. 14803/95.

Summary of the Invention It is an object of this invention to at least in part overcome the above-mentioned limitations on the range of possible designs of lever handles, and more generally to provide a novel configuration of latch drive assembly which is applicable to all forms of handle.

To achieve this object, the invention provides an arrangement by which it is possible to abandon the prior insistence on axial drive coupling of a handle to the latch drive spindle. This approach, and its configurational consequences, remain evident in the developments proposed in the aforementioned patents. In that respect, at least, the invention seeks to depart from this traditional requirement.

The invention provides, in a first aspect, a latch drive set including: a rotatable drive member having means for engaging the drive member with spindle means, for rotating the spindle means about an axis to operate a latch unit; mounting plate means for rotatably supporting said drive member with respect to the latch unit so that the drive member at least partly overlies the mounting plate means in the direction of said axis; and means on the drive member for coupling the drive member to a handle unit in an annular zone extending about said axis so that the handle unit at least partly overlies the drive member in the direction of said axis when so coupled; whereby, in situ, rotation of the handle unit is effective to rotate the spindle means via rotation of the drive member.

The drive member preferably includes a boss having a passage shaped to receive said spindle means, and a drive plate arranged to extend about the boss. The boss and drive plate can be separate portions, the plate receiving and being keyed to the boss.

The means for coupling the drive member to a handle unit preferably comprises bayonet coupling means.

The drive member preferably has a substantially flat outer surface which incorporates means for irrotationally attaching the handle unit.

In a second aspect, the invention provides a latch drive set including: a rotatable inner drive member adapted to be disposed within a passage formed in a panel and opening at a surface of the panel; means for engaging the inner drive member with spindle means, for rotating the spindle means about an axis to operate a latch unit; an outer drive member adapted to be disposed outside said passage to overly the inner drive member in the direction of said axis for substantially rigidly retaining a handle; and rotation transmission means for releasably and mutually irrotationally interengaging the drive members; whereby, in situ, rotation of the handle is effective to rotate the spindle means via rotation of the drive members.

The outer drive member can be an adaptor plate fitted to a handle, or can rigidly retain a handle by being formed integrally with the handle. The inner drive member may include a boss having a passage shaped to receive the spindle means, and a drive plate.

The rotation transmission means preferably comprises bayonet coupling means.

In both aspects of the invention, the bayonet coupling means can be at an outer rim of the drive member for engaging complementary means on a peripheral skirt of a handle unit, whereby the handle unit extends about the rim of the drive member and thereby substantially hides the drive member from view when the set is installed as an assembly on a door panel.

The latch drive set can further include a handle unit, and the bayonet mounting means can include deflectable arcuately extending tags on one of a drive member and the handle unit and complementary lugs on the other.

The handle unit can include a lever handle, although any style of handle is suitable for use with the invention.

There is preferably disengagable latch means for retaining the drive member and handle unit, or the two drive members, in coupled relationship. There is also preferably resilient means for returning the handle, after rotation thereof in at least one direction, to a neutral or centre position.

The means for rotatably engaging the drive member with the spindle means can include, for example, a socket of non-circular cross-section or a keyed engagement, preferably arranged to allow coupling of rotational motion in one direction only to an extent to permit independent rotation of the respective handles of a set of handles on opposite sides of a latch unit. The spindle means can be a spindle of non-circular cross section e.g. square or rectangular cross section.

It has also been recognised that the market requires that any range of door furniture products must include a privacy function for bathroom, toilet and bedroom applications. To this end, the invention preferably includes a novel privacy adaptor arrangement and, in a third aspect, provides a latch drive set having this feature. More specifically, the invention according to the first and second aspects preferably includes privacy adaptor means, which includes: a control unit for mounting at one side of the door panel and having finger operable setting means; a lock unit for mounting at the other side of the door panel selectively settable at a lock condition in which the handle unit at that side of the door is locked against rotation;

means for linking the control unit to the lock unit whereby finger operation of the setting means is effective to set the lock unit in its lock condition; and means in said control unit whereby rotation of the handle unit at said one side of the door releases the setting means and in turn, by virtue of the linking means, said lock condition, during said independent operative rotation of the handle unit at said one side of the door relative to the handle unit at said other side of the door.

In its third aspect, the invention provides for use in conjunction with a door latch set including a latch unit, drive spindle means, a pair of handle units adapted to be mounted at opposite sides of a door panel, and means for drivingly coupling the handle units to the spindle means so that the respective handle means independently rotate the spindle means without rotation of the other handle unit, a privacy adaptor set including: a control unit for mounting at one side of the door panel and having finger operable setting means; a lock unit for mounting at the other side of the door panel selectively settable at a lock condition in which the handle unit at that side of the door is locked against rotation; means for linking the control unit to the lock unit whereby finger operation of the setting means is effective to set the lock unit in its lock condition; and means in said control unit whereby rotation of the handle unit at said one side of the door releases the setting means and in turn, by virtue of the linking means, said lock condition, during said independent operative rotation of the handle unit at said one side of the door relative to the handle unit at said other side of the door.

In a fourth aspect, the invention provides a lever handle arrangement for turning an operative member of a door latch about an axis of rotation, said lever handle arrangement comprising a manually graspable portion at least a part of which is aligned with said axis of rotation.

Brief Description of the Drawings

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an exploded three dimensional view of the principal components of a basic door latch set incorporating a pair of latch drive assemblies formed from latch drive sets according to a first embodiment of the first and second aspects of the invention;

Figure 2 is an exploded view showing the components of one of the latch drive assemblies; Figure 3 depicts the door latch set installed in a door panel;

Figure 4 shows the installation of the fixing screws into one of the latch drive assemblies;

Figure 5 depicts the details of a bayonet coupling system for mounting a handle unit to the drive plate of the latch drive assembly; Figure 6 and 7 depict the engagement of the components of the bayonet coupling;

Figure 8 depicts the latch set of Figures 1 to 7 installed in a door panel, and shows three successive steps (a, b, c) in mounting a handle unit to one of the latch drive assemblies;

Figure 9 depicts a full installation of a latch set and handles with a privacy adaptor set in the locked position;

Figure 10 is an exploded view of the components of the door latch set of Figure 9 including the privacy adaptor set;

Figures 1 1 and 12 are schematic illustrations showing the functions of the privacy adaptor set; Figure 13 is an exploded three dimensional view of the principal components of a door latch set incorporating a pair of latch drive assemblies according to a second embodiment of the invention;

Figure 14 is a further exploded view showing the components of one of the latch drive assemblies of Figure 13; Figure 15 depicts the latch set of Figures 13 and 14 in situ in a door panel and shows a handle unit in position to be mounted to one of the latch drive assemblies; and

Figure 16 is a view similar to Figure 15 of a modified bayonet coupling for the embodiment of Figures 13 to 15.

Description of Preferred Embodiments Basic Set

In Figure 1, the illustrated door latch set 1 includes a latch unit 10 of conventional construction, a pair of similar latch drive assemblies 2a and 2b which are each formed from an individual latch drive set, and a latch drive spindle 18 of uniform rectangular cross section.

The two latch drive assemblies 2a and 2b are basically identical save for being a mirror image of each other and being of opposite rotation. Their main difference lies in their provision for assembly screws 19, one assembly having countersunk clearance holes 23 provided in the mounting plate 20, the other equipped with corresponding threaded holes 24 in bosses 25 of the opposing mounting plate. It is therefore proposed to describe only one of the assemblies and to identify the differences where appropriate.

Each latch drive assembly 2a,2b includes a mounting plate 20, a drive member 40 comprising an annular drive plate 30 about a boss 50, and a handle unit 70.

The mounting plate 20 is essentially a disc for covering the cross passage in the door panel and rotatably mounting the drive member 40. It may be produced as a metal die casting, a metal pressing or as a plastic moulding. Plate 20 comprises a flanged surface 21 which provides a clamping interface with the door panel, and has a circular central aperture 22 at its centre that serves as a bearing to accommodate a cylindrical body section 51 of drive boss 50. An integral central boss 29 projects on the reverse side (i.e. inside) of mounting plate 20 (Figure 1), its purpose being to laterally position a cam washer 65 (discussed further later) for its required function relating to the optional privacy adaptor assembly 100 (Figures 8 to 10) when this is provided. The raised arcuate land or annulus 27 provides a bearing surface at its interface with the drive plate 30. It also defines and bounds a space to accommodate a spiral leaf return spring 60.

Two arcuately spaced facing shoulders 28,29 project from the inner side of the raised land or annulus 27. Shoulders 28,29 interact with a projecting tag 36 of the drive plate 30 to define limits to the relative rotation of drive member 40 with respect to mounting plate 20 about axis 9. Shoulder 28 determines the 'at rest' position of the spring return rotational travel of the drive plate 30.

The drive plate 30 is ideally produced from spring steel and forms a sub-assembly with the drive boss 50 and the return spring 60. The cylindrical body section 51 of drive boss 50 forms a close fit with a central aperture 32 of the drive plate and rotational drive is transmitted via the engagement between integral key tags 33 of the drive plate adjacent aperture 32, and respective slots 54 in a flanged head 52 of the drive boss. The return spring 60 is assembled on the reverse side of the drive plate 30, between the drive plate and mounting plate and within land 27. The spring is concentric with the drive boss 50, with an end inner tag 61 of the spring engaging in a slot or hole (not shown) provided in the cylindrical section 51 of the drive boss. The outer hooked end 62 of spring 60 locates about an anchor spigot 26 projecting from the mounting plate 20 adjacent one end of land 27.

This sub-assembly locates with the mounting plate 20. The cylindrical section 51 of the drive boss 50 rotatably engages within the central aperture 22 of the mounting plate. With the end hook 62 of the return spring 60 engaged about spigot 26 of the mounting plate, the sub-assembly is rotated in the appropriate direction to pre-tension the return spring to ensure the engagement of the stop tag 36 of the drive plate with the rotational stop 28 of the mounting plate.

As already noted, the back or inside face of the drive plate locates against the raised land or annulus 27 of the mounting plate. The cylindrical body 51 of the drive boss projects beyond the end face 29a of the rear boss 29 of the mounting plate. Thus, the drive member 40 in part overlies the mounting plate 20. A central aperture 66 of the cam washer 65 engages with the projecting section of the drive boss, the two being rotationally keyed by engagement of an inner key tab 67 on the cam washer with a longitudinal keyway 55 of the drive boss. The inner face of the cam washer 65 locates

against the end face 29a of the rear boss 29, and a circlip 64 engages in a circular groove 56 of the drive boss to maintain the assembly of the drive member 40 with the mounting plate 20. The axial location of the circular groove 56 relative to the flanged drive boss head 52 is set to provide close contact between the assembled components when the circlip is engaged within the groove. The closeness of the contact between these components must allow freedom for rotational movement about axis 9 (within the limits set by the stops 28,29) while allowing only minimal lateral movement in the axial direction.

In Figure 3 the latch set is shown mounted on a door panel 5 concentric with a transverse or cross passage 6 which represents the trade standard 50mm diameter hole. The mounting plate is dimensioned to also cover a 54mm cross passage. A standard 22mm intersecting bore (not shown) may accommodate latch unit 10.

Latch unit 10 includes a facing plate 11 with apertures 12 by which screws 13 are employed to fasten the facing plate in a rebate at the edge of the door panel, thereby securing the latch unit in the door panel. The latch drive assemblies 2a and 2b are fitted, one on either side of the door at opposite ends of the transverse passage 6. They are coupled by the rectangular spindle 18 which passes through the passage 15 (Figure 1 ) of the latch unit 10 and engages at either end within shaped passages 53 of drive bosses 50 located within the keyed apertures 32 of the rotatable drive plates 30a and 30b.

The latch drive assemblies 2a,2b are fastened together by a pair of fixing screws 19 which pass through the countersunk holes 23 (Figure 2) in one assembly, and through holes 16 in the latch unit 10, and engage in threaded holes 48 of the other drive assembly. The screws draw the respective drive assembly mounting plates 20 together, clamping them firmly against the surfaces of the door panel about the open ends of the transverse passage 6. Either drive plate 30 transmits rotational movement to its respective drive boss 50 by means of the key tags 33, engaged in the slots 54 of the drive boss 50. Rotational movement is further transmitted to the rotatable sleeve 14 of the latch unit 10 via the rectangular spindle 18. Spindle 18 engages both the shaped passage 53 of each drive boss 50 and the rectangular passage 15 in the latch unit and, by virtue of a retractor

link (not shown) within the latch unit 10, rotation of spindle 18 is effective to retract latch bolt 17 behind facing plate 11 against an internal spring (not shown) biased to return the latch bolt outwardly.

By virtue of the shaped passages 53 of the two opposing drive bosses 50, the rotation of either latch drive assembly will transmit sufficient rotation to spindle 18 and to the latch unit to retract the latch bolt 17, without causing the other latch drive assembly to rotate. This feature of independent rotation of the latch drive assemblies is utilised in the functioning of the privacy adaptor assembly, discussed further below.

Figure 4 shows the proposed method of installing the two screws 19 into the latch drive assembly. The reasons for this slightly complex procedure are as follows. It is necessary, when installing the latch drive assemblies, to gain access to the heads of the fixing screws by means of a screwdriver in order to engage them with the corresponding threaded bosses of the other assembly. This access may be facilitated by means of appropriately located holes through the drive plate 30. However, if these holes are large enough to facilitate the installation of the screws through the drive plate there would then exist a possible safety hazard for this product in service. In the event of either of these screws 19 becoming loose, it would be possible for the screw head to engage within the hole provided in the drive plate and thus render the door locked. By the alternative provision of the smaller holes, large enough to provide access for a suitable screwdriver but too small to accommodate the screw head, this problem is prevented.

The solution to the above problem however generates another in the installing of the screws into the latch drive assembly. The screws could be pre-assembled into the appropriate latch drive assembly but the length of screws installed could not accommodate any variation of door thickness greater than 8mm. For this reason the person installing the product must be able to select and install the appropriate length of screw for the particular door being fitted.

To facilitate the above requirements, the following principles have been devised. In the left diagram of Figure 4, the drive plate 30 is shown rotated against the return

spring force to the second stop position defined by shoulder 29. At this point two larger holes 35 in the drive plate align with the countersunk screw holes 23 of the mounting plate. These holes 35 are large enough to allow passage of the heads of the screws 19. The screws are therefore inserted through holes 35 into the screw clearance holes 23 of the mounting plate, the heads passing through the clearance holes 35 of the drive plate to engage with the countersinks of holes 23 provided in the mounting plate. The drive plate 30 is then released, allowing it to rotate under spring pressure to the return stop position defined by shoulder 28 (right side of Figure 4). At this position two smaller holes 34 in the drive plate align with the screw heads allowing screwdriver access.

Figure 5 shows the inner features of a mounting base 71 of an integral handle unit 70 with a lever handle 79 designed to be detachably mounted to drive member 40 in a bayonet coupling arrangement. The normally circular base is recessed, defining a skirt 71a with an inner cylindrical wall 72 and an adjacent annular mounting surface 73. Four integral undercut lugs 74 are positioned around the inner wall 72. There is an opening 75 in the inner wall located non-symmetrically about the vertical centreline of the circular base and a recess 76 in the mounting surface 73 is located symmetrically about the vertical centreline. A projecting lug 77 located in the upper half of the handle base recess provides an abutment to transmit the rotational drive force from the handle to an opposed projection 85 of the drive member 30.

Four crescent shaped or arcuate deflectable tag members 81 , equispaced around the concentric with the rim of the drive plate 30, are inclined slightly 'away from the surface plane of the drive plate. A short section 82 at the free end of each crescent member is angled back towards the surface plane of the drive plate. Four notches 83 are provided beyond the end of each crescent member. A pawl is formed by a strip 84 extending radially downwards from near the central aperture of the drive plate. This strip is similarly inclined from the surface plane of the drive plate but opposite to that of the four crescent shaped or arcuate tag members 81.

Figure 6 shows the method of engagement of the bayonet coupling between the handle unit 70 and the drive plate 30 of the latch drive assembly. The four notches 83 of

the drive plate freely accommodate the four inwardly protruding undercut lugs 74 of the handle base. Rotation of the handle in the direction indicated by the arrow X engages the angled faces 82 of the crescent or tag members 81 with the underside faces of the undercut lugs 74. The ramp effect of the angled faces and the resilient nature of the material of the drive plate allows the crescent or tag members and the pawl 84 to deflect to conform with the fixed constraints of the undercut lugs and the reaction against the annular mounting face 73 of the handle. It will be appreciated that tag members 81 with notches 83 and lugs 74, together form means for rotatably coupling the handle unit 70 to drive plate 30 in an annular zone extending about axis 9. Drive plate 30 may be considered to provide a platform to which the handle unit may be detachably fixed. There is no central socket for drive spindle 18, thus freeing the handle designer from the restraint of designing from the need for such a socket.

Figure 7 shows the handle unit 70 fully engaged with the drive plate 30. In this relationship the pawl 84 engages the recess 76 simultaneously with the abutment of the complementary lug 77 of the handle base and projection 85 of the drive plate. The engagement of the pawl 84 within the recess 76 prevents reverse rotation and consequent disengagement of the bayonet mounting of the handle. To remove the handle, the pawl 84 is deflected with a suitable tool to disengage it from the recess 76 to allow reverse rotation to disengage the bayonet coupling.

It will be appreciated that, once the handle unit 70 is engaged and locked onto the drive plate 30, and with the lever handle 79 in its normal horizontally extending, i.e. neutral or centre, position, downward rotation of the handle 79 will be effective to rotate drive spindle 18 via drive member 40, and thereby to withdraw the latch bolt 17. Return of the handle 79 to the centre level position is assured by the coil spring 60 retained within the latch drive assemblies 2a and 2b.

Figure 8 sequentially illustrates the mounting of a handle unit to a latch set installed into a door panel. Figure 8a shows the latch set mounted in a door panel with the appropriately handed handle 70 at a particular rotational position to be presented for engagement with the drive plate 30. In Figure 8b the handle is shown engaged with the

drive plate, the pawl 84 being accommodated within the recess 76 of the handle base. The handle unit 70 is pressed firmly against the drive plate 30 and rotated in the direction of arrow X to engage the bayonet coupling. The rotation of the handle induces the drive plate to rotate and withdraw the bolt (this movement has been omitted from the illustrations to simplify the description) but further rotation of the handle is required to fully engage the bayonet coupling. Figure 8c shows the handle unit fully engaged with the latch drive assembly, the pawl 84 being engaged within the recess 76 to prevent removal of the handle unit by opposite rotation. Removal of the handle is effected by deflecting the pawl 84 with a suitable tool to disengage it from the recess 76, thus allowing contra-rotation and disengagement of the bayonet coupling.

Figure 8 also well illustrates how, in the assembled condition of the latch drive set, the handle unit 70 extends about the rim of drive member 40 and substantially hides it from view.

It will be appreciated that there are many handle coupling or mounting arrangements which could be employed as an alternative to the bayonet coupling described above. Two such alternative bayonet coupling arrangements are described hereinafter, with reference to Figures 13 to 15 and to Figure 16.

It will be apparent to those skilled in the door handle arts that the handle units 70 and 70' (Figure 15) differ from conventional handle levers in a significantly different aspect. With conventional handle levers, the lever is supported by a spindle or axle (or a housing therefor) at one end, the lever being a cantilever which rotates about an axis of rotation passing through both the axle (or axle housing) and the end of the lever. Thus the manually graspable portion of the handle lever is displaced sideways from the axis of rotation. As a consequence, the torque applied to the axle or spindle, is generated by a (normally downwardly directed) force which is displaced from the axis of rotation by a short distance which is typically about half the length of the handle.

In the present arrangement, however, the manually graspable portion of the handle 70 or 70' is aligned with the axis of rotation because the handle lever itself is supported

by an L- or U-shaped portion which is displaced from the axis of rotation. Thus the force of the hand acting on the handle lever itself is more in the nature of a couple in that the little finger (and adjacent fingers of the hand) exert a downwards force on the upper surface of the handle lever itself whilst the thumb exerts an upwardly directed force on the lower surface of the handle lever. These two forces are applied on opposite sides of the axis of rotation.

This is quite different from a conventional lever door handle since no force is exerted on the lower surface of a conventional lever door handle.

Furthermore, since the L- or U-shaped portion which connects the lever handle itself to the remainder of the door latch can be of any shape or dimension, this permits the handle portion 70 to be substantially centrally positioned relative to the axis of rotation of the handle (as seen in Figures 6 or 8 for example). By way of contrast a conventional lever door handle always has the manually graspable lever positioned only to one side of its axis of rotation.

Finally, it will be apparent that the L- or U-shaped portion which supports the lever handle can merge with the circular mounting base 71 so as to form a rotatable cover or escutcheon which conveniently hides the remainder of the latch mechanism from view.

Privacy Adaptor Set

An optional privacy adaptor set for the door latch set of Figures 1 to 8 will now be described with reference to Figures 9 to 12. This privacy adaptor set may be readily applied to a variety of other latch sets. Accessories of this kind are considered to be an important option, in order to provide a privacy locking function for a latch drive set installed in a bathroom or toilet door.

Ideally, a privacy adaptor set provides the facility for a door to be "snibbed" or locked from inside a room e.g. a toilet or bathroom to prevent the entrance of other persons. It is also desirable to include an emergency release function, i.e. a safety override which allows release from the locked condition to be effected from the outside

of the door by the use of a simple tool such as the tip of a pencil or similar. A third desirable feature is to include an automatic release function whereby the normal operation of the door handle on the inside of the room will disengage the lock mechanism without any need to first disengage the snib.

Figure 9 shows a privacy adaptor set 100 as it would be installed with the latch drive set 1 complete with handles. The set includes a control unit 1 10 and a lock unit 120 on opposite sides of the door, operatively coupled by a link rod 1 16 which transmits rotation from a trigger 102 of the control unit to a locking arm 122 of the lock unit. Appropriate areas are illustrated cut away to show the inner mechanism of the privacy function. An exploded view which illustrates the relationship of the separate units as required for installation is depicted in Figure 10. Control unit 110 is on the near side in these views, but the privacy set is ambidextrous and can equally well be installed with the units 1 10 and 120 on the opposite sides to that shown. This provides the option of installing the privacy set with the control unit 110 mounted on the appropriate side of the door.

Privacy control unit 1 10 is normally installed on the inside face of the door. This unit comprises four components, a circular peripherally flanged housing 1 1 1 and the trigger 102 (which would ideally be produced as metal die castings or plastic mouldings), a bow-shaped indexing spring 109 and a cover plate 1 18 (Figure 10). Lock unit 120 is normally installed on the outside face of the door and comprises three components, a circular peripherally flanged housing 121, the locking arm 122 and a cover plate 128. Both housings 1 11,121, of units 110,120 respectively, and cover plates 1 18,128 are provided with two holes 1 14 which engage on installation with the protruding fixing screw bosses 25 of the respective latch drive assemblies. The close fit of these items controls the concentric relationship between the individual units. Each unit 1 10,120 of the privacy set is installed with the cover plate 1 18,128 facing the back face of the respective latch drive assembly, a shaped central aperture 1 17 allowing entry into the housing of the cam washer 69.

With reference in particular to Figure 1 1 , the trigger 102 pivots about a boss 103 which locates in a complementary hole provided in the back wall of housing 1 1 1. The boss 103 has a square or appropriately non circular passage 104 concentric with the boss axis for receiving link rod 116. The main profile of the trigger is designed to provide a head 108 which protrudes outside the housing via aperture 1 19 to provide access for actuation by depression with a finger tip. In the locked position the angled or V-shaped projection 105 intrudes within the rectangular notch 68a of the cam washer 69a at that side of the door. A "V" notch 107 accommodates one end of indexing spring 109, the other end being engaged within a similar "V" notch 1 15 in the inner rim 1 13 of the housing 1 11. The indexing spring is a bow or omega shaped strip of spring steel, of a rectangular cross section. It is compressed lengthwise to engage with the two notches 107 and 1 15 and causes the trigger 102 to snap either side of a centre line between the pivot point 103 and the V notch 1 15.

The locking arm 122 is similarly pivoted about a boss 123 with a square passage

124 for link 116. The arm provides a rectangular dog 125 which, when the arm is set to the locking condition, engages notch 68b of cam washer 69b at the outside of the door, to lock the latch drive assembly at this side against rotation.

A safety override function is provided to unlock a door from the outside by the provision of an access aperture 127 in the outer rim of the housing 121. The locking arm 122, when in the locked position, can be engaged through the aperture 127 with a suitable tool and so pressed downwards to cause the arm to rotate and disengage dog 125 from the cam washer.

Square-section apertures 104,124 are coupled by link rod 116 of matching cross- section. The engagement of these two elements with the common link rod ensures that the movement of the trigger 102 controls the positioning of the locking arm 122.

The two matching positions of the units are shown in Figures 11a, l ib and 12a and 12b. When the trigger 102 is set down (Figure 1 la), the locking dog 125 is engaged, rendering the door locked to entry from that side. Actuation of the handle on the inside

latch drive assembly causes the cam washer 69a to rotate, bringing one corner of the rectangular notch 68a of the cam washer into contact with one edge of the V-shaped projection 105. Further rotation lifts this projection, causing the trigger 102 to rotate about its pivot boss 103 to a position where the indexing spring 109 passes beyond the centreline of its operation. At this point the spring drives the trigger to fully disengage from the cam washer and come to rest with the stop face engaging the inner rim 1 13 of the housing 1 1 1. This movement of the trigger is transmitted via the link rod 1 16 to the locking arm 122 of the opposing side to disengage the dog 125 of the locking arm from the rectangular space 68b of the cam washer 96b, thus freeing the outside latch drive assembly for normal functioning.

The privacy adaptor set thereby has the desired automatic release function. It will be appreciated that the rotation of the inside handle to effect automatic release is possible because of the aforementioned independent rotational drives of the two handle units : the shape of spindle socket openings 53 permits the spindle to rotate in the reverse direction at either boss 50 without rotating the respective handle unit.

Alternative Assemblies

Figures 13 to 15 illustrate an alternative embodiment of the invention, utilising a pair of individual latch drive sets in which the mounting plate embraces the drive plate, and in which the handle unit includes an adaptor plate for a face-on bayonet engagement with the drive plate. In Figures 13 to 15, like features are indicated by like primed reference numerals relative to the embodiment of Figures 1 to 8.

The door latch set 1' of Figures 13 to 15 includes a latch unit 10' of conventional construction, a pair of similar latch drive assemblies 2a',2b', and a latch drive spindle 18' of uniform square cross section. The latch set 1' is mounted in a door panel as shown in Figure 15 by forming a transverse spindle passage normal to an intersecting bore for the latch unit. The arrangement is similar to that for the first embodiment.

Each latch drive assembly 2a',2b' includes a generally annular mounting plate in the form of a housing 20' which extends about and partially encloses an inner latch drive

member 40' comprising a generally circular drive plate 30' having the configuration of a flange-rimmed disc, and a drive boss 50'. Housing 20' is cast in aluminium or a suitable alloy and is wholly open at its outer axial end but closed at its inner axial end except for a central aperture 22'. An outer flange 20a extends peripherally about the open outer end of housing 20', while an inner co-axial flange 20b about aperture 22' defines a bearing for complementary drive boss 50' projecting co-axially from one side of drive plate 30'. Boss 50' projects through aperture 22' and has a central square section blind bore 53' serving as a socket for rotatably engaging drive plate 30' with spindle 18' for operating latch unit 10'. A bearing bush 22a of a suitable material is fitted between the bearing surface of flange 20b and boss 53' and includes a peripheral thrust flange 22b between the face of drive plate 20' and the edge of flange 20b. Outside housing 20', a flat thrust washer 20c is carried by boss 50', and the assembly of the housing and the drive plate is maintained by a circlip 64' disposed in a matching groove 56' in the boss

The latch drive assembly 2a',2b' is disposed in an open end of the spindle cross- passage in the door panel, with flange 20a engaging the surface of the panel about the open end of the passage, as seen in Figure 15. Drive plate 30' is located with its main outer face 31 substantially flush with the outer face of flange 20a and its peripherally extending flange rim 33 projecting a little outwardly from this plane. Fixing screws 19' are passed through unthreaded countersunk apertures 23' in one of the housings 20' to engage threaded apertures 24' in the other housing. Drive plate 30' has a pair of scallop cut outs 49 to accommodate passage of the fixing screws 19'.

A wide variety of designs of handle unit 70' may be fitted to drive plate 30' by means of a bayonet coupling between the drive plate and a complementary adaptor plate 200 (Figure 15) exposed on the rear face of the handle unit. Adaptor plate 200 acts as an outer latch drive member and is attached to the handle by screws, rivets or the like at holes 21 1. Since the design of the handle unit itself maybe highly variable, and in order to better illustrate the bayonet coupling, the handle unit is shown only in outline in Figure 15.

In this case, the bayonet coupling comprises a trio of equiangularly spaced radially out-turned rectangular lugs 74' projecting from the otherwise flat outer face 31 of drive plate 30', and three matching arcuately extending cut outs or apertures 83' in adaptor plate 200. As can be seen from the drawings, apertures 83' have an enlarged end 83a to which may be applied lug heads 74a as depicted in Figure 15, at a particular rotational position. The handle is then rotated downwardly to its correct horizontal position, the lugs move back along the narrower portions of apertures 83' so that the heads 74a of the lugs are in front of and engaging the adaptor plate, whereby the handle unit is held in position. At this point, the lugs 74' are at the end of the apertures 83' and further downward rotation of the handle will cause the drive plate to rotate with the handle. Correct engagement and coupling of plates 30', 200 is further facilitated by co¬ operation of a central annular pin 202 on drive plate 301 with aperture 203 in adaptor plate 200.

Means is provide for releasably latching the handle unit in place. This means includes a pawl 84' formed by defining an arcuately extending strip 204 at the periphery of adaptor plate 200. The strip 204 is defined by an arcuate concentric slit 206 in plate 200, and by a notch 208 at one end of slit 84b. The strip 204 is provided at this end with a radially outwardly extending tab portion 210 which projects through a slot at the edge of handle unit base 201. The pawl 84' is deformed to an equilibrium position inclined to the plane of plate 200 so that the tab portion 210 normally lies against the front face of plate 301 in a slot 212 formed by a discontinuity in rim 33. Relative rotational motion of drive plate 30' and adaptor plate 200, which would disengage the bayonet coupling, is thereby prevented by the locking of pawl 84' in slot 212. The material of adaptor plate 200 is a resiliently deformable spring steel : by using a finger or tool to push and temporarily hold tab 210 out of slot 212, the handle unit 70' can be rotated counter¬ clockwise and withdrawn to disengage the bayonet coupling.

It will be appreciated that, once the handle unit is engaged and locked onto the drive plate 30', and with the handle in its normal horizontally extending i.e. neutral or centre, position, downward rotation of the handle will be effective to rotate drive spindle

18', and thereby withdraw the latch bolt, via rotation of adaptor plate 200 and inner drive member 40'.

Return of the handle to the centre position is assured by a coil spring 60' which is retained within housing 20' in the space about flange 20b. The out-turned end portions 62',61' of the spring are respectively held between lands 26a,26c of housing 20', and behind a substantially lug 61a disposed on the rear of drive plate 30' radially outwardly from boss 50'. Land 26a is one of the pair of similar diametrically opposite lands 26a,26b in which apertures 23' for fixing screws 19' are formed. Land 26c is a partial radial partition spaced slightly circumferentially from land 26a.

As the handle is depressed, and drive plate 30' rotated, lug 61a moves around towards land 26a and compresses spring 60'. Land 26a also forms a stop limiting movement of the handle, while the horizontal centre position is defined when lug 61a, returned by the spring, strikes a further land 60a formed at the interior top of housing 20'.

A modified bayonet coupling for the embodiment of Figures 13 to 15 is illustrated in Figure 16. Like features are indicated by like double-primed reference numerals.

In this modified bayonet coupling, four equispaced arcuate lugs 74" project inwards from the flange rim 33" of drive plate 30". These lugs provide an undercut feature which accurately engage with four matching tags 81 " formed as part of the adaptor plate 200". These lugs are extended from the face of the adaptor plate 200" by a precise distance to engage the underside of the lugs 74"

As depicted in Figure 16, at a particular rotational position the handle is presented to the mounting face of the drive plate 30". The extended tags 81" of the adaptor plate 200" are accommodated in the spaces between the lugs 74" of the drive plate 30". The handle is then rotated downwardly to its correct horizontal position. The tags 81 " of the adaptor plate 200" engage with the inner undercut faces of the drive plate lugs 74" and abut the endstops 220 whereby the handle unit is held in position. A deformable pawl

84" similar to that of the first embodiment engages a recess 76" to releasably latch the handle unit in place.

It will also be appreciated that, in its broadest aspects, the invention extends to handles and knobs other than lever handles. The illustrated embodiment eliminates the major constraint on door handle designs in that with these principles there is no need to design handles around a requirement to provide a socket to directly receive the spindle. All manner of moulded or cast shapes of handle can be applied to the more generous mounting facility proposed.

It will also be understood that the term "comprises" or its grammatical variants as used herein is equivalent to the term "includes" and is not to be taken as excluding the presence of other elements or features.