AU719859B2 - Door latch mechanism - Google Patents

Description

WO 98/21432 PCT/AU97/00769 DOOR LATCH MECHANISM Field of the Invention This invention relates generally to door latch arrangements which are especially useful where designed to fit within the standard 22mm diameter bored hole commonly used for the mounting of door latch mechanisms.

Background Art The practice of accommodating door latch mechanisms in a 22mm diameter hole is a simpler and cheaper method of installing door latches than the more traditional mortice type which requires a deep rectangular cavity to be cut in the edge of the door.

However, the 22mm bored hole imposes restrictions on the design of latch mechanisms as it limits the space available to accommodate the components which convert the rotary action of the door handle to the linear action required to withdraw the latch bolt.

Because of this limitation, manufacturers of these latch assemblies employ a type of cam action to retract the latch bolt in one such arrangement, rotatable cam lobes engage the edges of slots or other openings in a retractor carriage. The cam is designed to retract the latch bolt with minimum rotation of the handle, but it is difficult to achieve anything less than 550 of rotation for the 1 mm of travel typically required.

PCrIAU 9 7 0 0 7 6 G 2 RECEIVED 1 C, These mechanisms using a cam action are therefore less than satisfactory in that they result in the need for excessive rotation. This is particularly undesirable when used with lever handles. The cam action also generates a high degree of friction which results in rapid wear rates and a reliance on lubrication of the cam action. This friction also increases the force required to operate the door latch.

It is generally recognised that a latch unit should preferably be ambidextrous, that is adaptable to doors which open from either left or right. This requirement is met in most cam-operated designs by installing the latch unit with the ramp side of the latch bolt facing in the appropriate direction. These latch units are usually designed with a double acting cam action which withdraws the latch with either clockwise or anticlockwise rotation of the door handle. In this way, left or right hand installation is catered for.

Lever handles are usually restricted in their rotation by an inbuilt spring return mechanism which returns the lever to a horizontal stop position. The latch is actuated by a downward movement of the lever which generates rotation in one direction. When door knobs are used there is no requirement for separate spring return arrangements so that a knob may be turned in either direction to actuate the door latch.

Summary Of The Invention The invention provides a latch mechanism for a door, the mechanism including: a housing adapted to fit within a 22 mm diameter bored hole; a latch bolt unit supported in the housing for movement between an extended and a retracted condition, said latch bolt unit carrying a pin means; means rotatably mounted in the housing and configured for engagement with a handle shaft for rotation of said rotatably mounted means about an axis by said handle shaft, said rotatably mounted means carrying another pin means; and an elongate link having a pair of elongate slots each pivotally engageable with one of said pin means for coupling said latch bolt unit and said rotatably mounted means whereby rotation of said rotatably mounted means by said handle shaft engaged therewith is effective to move the latch bolt from its extended to its retracted condition, said elongate link pivotally engaging the rotatably mounted means laterally of said axis, wherein said pin means are each slidable along their respective one of said slots to allow the latch bolt unit to be pushed back from the extended to the retracted condition on closing the door.

The mechanism preferably further includes means for biasing the latch bolt unit to the extended condition, e.g. a spring acting between the housing and the latch bolt unit.

AMEI"f DO SHEET ,IPEA/AU IN:\LIBdI00614:DMB PCT/AU 9 7/00769 RECEIVED 1 3 AU" !"93 Preferably, the movement of the latch bolt unit is along a generally horizontal line of symmetry with respect to the latch bolt unit, which line contains said axis.

In an embodiment, the rotatably mounted means includes a lever.

The rotatably mounted means may be configured for engagement with a handle shaft and rotation about an axis by the handle shaft by having a socket or bore to receive the handle shaft or a pair of handle shafts so as to be keyed to provide rotation with the shaft(s).

The housing may include a first section in which the latch bolt unit is close sliding fit, and a second section with one or more apertures to provide said rotatable mounting.

Advantageously, the engagement between the rotatably mounted means and handle shaft(s) is provided for by a socket or bore which is a lost motion coupling when the shaft is rotated in the direction opposite to that which is effective to retract the latch bolt unit.

The latch housing may be produced as a metal diecasting, a plastic moulding, a fabrication of pressed metal components or any combination of these.

N AM1dDO SHEET OFO IPEA/AU [N:\LIBd]00614:DMB WO 98/21432 PCT/AU97/00769 4 Brief Description of the Drawings The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a three dimensional view of a door latch unit according to an embodiment of this invention; Figure 2 is a longitudinal cross-section of the door latch unit installed in a door, viewed in an off-centre vertical plane in the "at rest" position; Figure 3 is a similar cross-sectional view to Figure 2, but without the door; Figure 4 is a view similar to Figure 3, but with the unit shown in the fully retracted position; Figure 5 is a view similar to Figure 4 but with the bolt depressed within the latch case, representing the action when a door is closed without operation of the handle; Figure 6 is a view similar to Figure 4 but showing the transition from one hand operation to the opposite; Figure 7 is an alternative embodiment of the door latch unit, modified to overcome the possible effects of incorrect installation; and Figure 8 is a view similar to Figure 7 but depicting the outcome of an incorrect installation.

Detailed Description of Embodiments of the Invention The door latch unit 10 illustrated in Figures 1 to 6 includes a housing or latch case 11 which comprises a tubular outer section 12, defining a bolt chamber and having the usual front mounting plate 13, and an inner or rear section 14. Rear section 14 has a pair of spaced side plates 14a, 14b which provide respective aligned location apertures 15 for a rotatable lever member 18 disposed between the plates. Outer case section 12 mounts latch bolt unit 27 in a close sliding fit, for movement between an extended (Figures 2 and 3) and a retracted (Figure 4) condition.

The location apertures 15 provide a clearance fit with the respective bosses 19 at each side of the rotatable lever member 18. This clearance is provided to allow alignment of the rotatable lever member with the handle assembly when installed in a WO 98/21432 PCT/AU97/00769 door. Apertures 15 mount lever member 18 for rotation about an axis 15a at the centres of the apertures.

Latch case side plates 14a,14b further include two pairs of aligned holes 16 to provide passage for two screws 40 (Figure 2) which are sometimes used for the attachment of certain types of door furniture. These holes are also laterally elongated or elliptical (best seen in Figures 3 to 5) to accommodate a measure of misalignment with location of the door handle assembly when mounted on a door. The location and size of these holes 16 are a trade standard.

Two countersunk holes 13a are provided in the front plate 13 for receiving respective screws 31 to secure the latch assembly into a preferred cavity in a door 9.

In Figure 2, the latch unit 10 is shown as installed in a door, and is depicted in the "at rest" position. Because of the protrusion of the linkage mechanism at 43 (to be further described), a transverse hole 45 of 50mm minimum diameter is required to be drilled through the door concentric with the rotatable member 18. However, a trade standard hole size of 54mm is often required to mount many types of door furniture at the same location. A standard 22mm hole 47 is drilled into the door edge to intersect hole 45, and to accommodate the outer section 12 of latch case 11.

Rotatable member 18 is in the form of a lever and is provided with a squaresection centre hole 20 concentric with bosses 9. The square hole 20 is of a suitable size to engage with a typical square-section drive shaft (not shown) appropriate to engage with a handle assembly. The square-section shaft passes through the latch boss hole to engage the relevant handle assemblies, one mounted on each face of the door.

Rotatable lever member 18 projects radially of axis 15a and is tapered outwardly.

Adjacent its outer end are a pair of co-axial oppositely projecting spigots 22 aligned parallel to bosses 19. Means is provided in the form of an elongate link 23, for coupling the latch bolt unit 27 and lever member 18 whereby rotation of the latter by a handle shaft WO 98/21432 PCT/AU97/00769 6 engaged therewith is effective to move the latch bolt from its extended to its retracted condition.

Connecting link 23 can be seen in Figure 1 to have a clevis 50 at one end that embraces lever member 18 and has respective longitudinal slots 52 in its clevis arms 51 which engage with the lever spigots 22. At the opposite end (Figure 3) is a shorter longitudinal slot 54. This slot provides a pivotal attachment point with the bolt unit 27 by means of a transverse pin 26 accommodated within a hole passing through the bolt unit at that point. Link 23 is accommodated within a central slot or recess 28 provided in the bolt unit and located at its vertical centreline.

A helical compression return spring 29 is located in a recess 30 provided in the back end of the bolt unit. The other end of the spring reacts against the adjacent inner end wall 32 of case section 12. The recess 30 in the bolt unit is of sufficient size to accommodate the spring when the bolt is retracted into the latch case.

Figure 4 shows the latch unit in the actuated position, that is when the door handle is turned to retract the bolt into the latch case. In this view the rotating lever member has been rotated by 45 degrees about the axis 15a of the bosses 9. The pivot connections of the lever member 18 and bolt unit 27 with the link 23 cause the bolt unit 27 to be drawn into the latch case. Spring 29 is compressed during this retraction movement, and on release of the handle drives the bolt unit back to the extended position.

Figure 5 shows the bolt 27 depressed into the housing during the action of closing the door without the use of the handle to withdraw the bolt. This action results from the engagement of the ramped face 33 of the bolt with the striker plate of the door frame (not shown). This view shows the purpose of the slots 52 and 54 in allowing relative linear displacement at the respective pivotal connections, thus permitting the bolt unit 27 to be depressed into the latch case chamber 12 without transmitting any force back through the lever member 18 to the handle mechanism.

WO 98/21432 PCT/AU97/00769 7 The installation of a door latch unit requires that it is appropriately oriented to suit the particular direction of door opening. This requires that the ramped face of the bolt must engage with the striker plate of the door frame when closing. The latch unit can be installed to suit either direction by rotating it along its longitudinal axis to achieve the required orientation. As this latch unit does not have an ambidextrous action it is necessary to set the action of the mechanism for the correct direction of rotation after the latch unit has been installed.

Figure 6 shows a provision for setting the latch unit for the required direction of rotation. For the latch unit to be inserted into the 22mm diameter hole 47 bored in the door it is necessary for the lever members 18 and the link 23 to be depressed below the profile of the latch case. The slots 52,54 allow this movement. When the latch has been installed, the lever member 18 is rotated to the correct "at rest" position (Figure 3) before proceeding with the fitting of the drive shaft and handle assemblies.

An alternative configuration of the drive mechanism is illustrated in Figure 7, and is intended to overcome the possibility of damage resulting from incorrect orientation of the lever and link components on installation. Figure 7 shows the modified latch unit correctly oriented for operation. In place of the square drive hole which passes through the bosses 19 of the lever member 18 as depicted in Figure I, there is a shaped passage This passage is essentially of a cylindrical form 62, concentric with the boss diameter and separated into two sections by two abutments 64 which provide respective faces 66 that engage with a rectangular handle drive shaft 65. This drive shaft transmits the rotary force from the handle(s) to the rotatable lever member 18'. As rotation of this member is only required in one direction (clockwise as viewed in Figure 7) in order to withdraw the bolt unit 27 into the bolt chamber 12, space 70 is provided (by virtue of abutments 64 and the rectangular shape of shaft 65) to allow freedom for the drive shaft to rotate in a lost motion for 60 to 70" in the opposite direction within the passage 60 without transmitting any rotational force to the lever member.

In a correctly installed assembly there is no need for any rotation in the opposite direction. But in the event of an incorrect installation, the provision of the space 70 for WO 98/21432 PCT/AU97/00769 8 opposite rotation serves to remove the risk of damage to the link 23' or other parts of the latch unit. In Figure 8, the latch unit is shown with the link 23' and the rotatable lever member 18' incorrectly installed. The drive shaft 65 is shown rotated in the direction which would result from normal operation of the door handle. The space 70 provided within the shaped passage 60 accommodates the rotation of the drive shaft 65 without transmitting any movement to the lever member 18', thus avoiding any risk of damage to other components of the latch unit.

In this example, this driving member is in the form of a square section shaft which passes through a close fitting square hole provided in the centre of the boss. However, other suitable shapes can be used.

The preferred embodiments of the invention possess several advantages over prior art devices. Firstly, the pivot link arrangement requires less operating force than devices employing a cam action. Further, the pivoted link has greatly reduced frictional wear compared to cam action latches, thereby increasing its operational life.

Secondly, the reduced rotation of the handle provides a more solid and higher quality feeling latch which is attractive to purchasers.

Thirdly, some countries require external door mortice locks to have an operating handle with a 450 operating rotation. The preferred embodiments of the invention meet this requirement and, as they are also suitable for passage door latch mechanisms, they allow reduced inventory for lock/latch installers and provide consistent operation and appearance throughout a dwelling.

Although the invention has been described with reference to preferred embodiments, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (3)

1. 9- CLAIMS 1. A latch mechanism for a door, the mechanism including: a housing adapted to fit within a 22 mm diameter bored hole; a latch bolt unit supported in the housing for movement between an extended and a retracted condition, said latch bolt unit carrying a pin means; means rotatably mounted in the housing and configured for engagement with a handle shaft for rotation of said rotatably mounted means about an axis by said handle shaft, said rotatably mounted means carrying another pin means; and an elongate link having a pair of elongate slots each pivotally engageable with one of said pin means for coupling said latch bolt unit and said rotatably mounted means whereby rotation of said rotatably mounted means by said handle shaft engaged therewith is effective to move the latch bolt from its extended to its retracted condition, said elongate link pivotally engaging the rotatably mounted means laterally of said axis, wherein said pin means are each slidable along their respective one of said slots to allow the latch bolt unit to be pushed back from the extended to the retracted condition on closing the door. 2. A latch mechanism according to claim 1 further including means for biasing the latch bolt unit to the extended condition. 3. A latch mechanism according to claim 2 wherein said biasing means includes a spring acting between said housing and said latch bolt unit. 4. A latch mechanism according to claim 1, 2 or 3 wherein said pin means carried by the rotatably mounted means includes a pair of spigots which engage respective slots in the arms of a clevis portion of said elongate link. A latch mechanism according to claim 4 wherein said latch bolt unit has a central slot at its inner end within said housing to receive an end of said elongate link having one of said slot means, said pin means which engages that slot means extending transversely of said central slot. 6. A latch mechanism according to any one of the preceding claims wherein said movement of said latch bolt unit is along a generally horizontal line of symmetry with respect to said latch bolt, which line contains said axis. 7. A latch mechanism according to any one of the preceding claims wherein said rotatably mounted means includes a lever. 8. A latch mechanism according to any one of the preceding claims wherein the rotatably mounted means is configured for engagement with a handle shaft or a pair of handle shafts and rotation about an axis by the handle shaft(s) by having a socket or bore to receive the handle shaft(s) so as to be keyed to provide rotation with the handle shaft(s). SHEET IPEA/AU [N:\LIBd]OO614:DMB 9. A latch mechanism according to any one of the preceding claims, wherein said housing includes a first section in which said latch bolt unit is a close sliding fit, and a second section with one or more apertures to provide said rotatable mount.
2. 10. A latch mechanism according to claim 7, 8 or 9 wherein said housing second part has spaced parallel side plates, and said lever is disposed between those side plates and has a pair of bosses to engage respective apertures in said side plates.
3. 11. A latch mechanism according to any one of the claims 1 to 7 wherein said engagement between said rotatably mounted means and a handle shaft or a pair of handle shafts is provided for by a socket or bore which is a lost motion coupling when the handle shaft(s) is/are rotated in the direction opposite to that which is effective to retract the latch bolt unit. ZCT 0-MZD SHEET !PEA/AU [N:\LIBd00614:DMB