A conventional doorlatchcomprises ahousing, known as a lock case, with a bolt biased out of a fore end of the housing. A follower mounted for rotation within the housing converts rotational movement from ahandle mounted externally of the housing, to rectilinear movement of the bolt in a direction into the fore end of the housing.

One conventional door latch housing is substantially rectangular in cross section, and therefore requires an elongate mortise to be chiselled or machined in the edge of the door to receive the housing during fitting. Holes are drilled in either side of the door, perpendicular to, and in communication with the elongate mortise for receiving a square section latch driving spindle which is connected in driving engagement between door handles on either side of the door and the follower.

In order to attach the latch housing to the door, a plate is mounted at the fore end of the housing, and woodscrews are driven through holes provided in the plate into the edge of the door. The surface of the plate facing outwards ofthe door is fitted flush with the door edge, and consequently a recess must first be chiselled in the edge ofthe door to receive the depth of the plate. Preparation of a door for the fitting of a latch requires the labour of a skilled tradesman, and is therefore costly.

The maj ority of me work is usually carried out by hand, and the risk of making an error, resulting in the scrapping of a door is high.

Typically, when opening a door fitted with a conventional door latch, the door handle must be moved through a significant arc in order to withdraw the bolt into the latch housing, which maybe 60° or more.

It is an object of the invention to provide a door latch which is easier to fit and operate than a conventional door latch of the kind described above.

According to the present invention there is provided a door latch comprising a follower mounted for rotational movement in a latch housing, a multiplier operatively linked to the follower for amplifying rotational movement of the follower, a bolt biased outwards of the housing, and an inelastic flexible element connected between the multiplier and bolt for converting rotational movement of the multiplier to rectilinear movement of the bolt.

It is an advantage of the invention that the latch housing can be fitted in a circular bore, which negates the need for skilled chiseling of a door during fitting of the latch. It is a further advantage that when opening a door fitted with a door latch ofthe invention, the door handle need only be moved through an arc of 20°.

Preferably, the follower has a spring arm and an actuating arm extending from opposite sides of a central hub. The hub preferably locates in circular apertures provided in either side of the latch housing. A square aperture maybe provided through the follower in axial alignment with the hub for receiving a square section latch driving spindle of a door handle in conventional manner.

Preferably, a guide pin is mounted on the actuating arm of the follower, and the multiplier is provided with a pin guide surface. The pin guide surface may be straight or curved, but is preferably evolute. The guide pin preferably cams against the pin guide surface.

The multiplier is preferably mounted for rotation about a pivot.

One end of the inelastic flexible element maybe connected to the bolt by means of a ball and socket joint. The other end ofthe inelastic flexible element maybe provided with a substantially circular enlargement, which is received and retained in a correspondingly shaped recess in the multiplier.

Preferably, the inelastic flexible element is provided with aball or cylindrical member, which engages in a socket provided in the bolt. The ball or cylindrical member may be located in the socket during assembly of the joint as a snap fit.

Preferably, a circular recess is provided in the end ofthe bolt, which receives a spring for biasing the bolt outwards of the housing. The spring reacts against an internal wall ofthe housing. The socket may extend from the circular recess into the bolt, and is preferably concentric with the recess.

The multiplier has an outside edge which maybe straight or curved, but is preferably involuted.

During opening ofthe latch, the inelastic flexible elementmaywrap around the involuted outside edge of the multiplier.

A handle return spring maybe provided which acts between the spring arm ofthe follower and the housing. The handlereturn springpreferablybiases the followertowardsapositioninwhichthe bolt is extended from the housing, and the door handle operating the latch is in a rest position.

Preferably, the end ofthe bolt which extends from the housing is provided with upper and lower flats. The flats maybe guided by correspondingly shaped flats provided in an aperture, through which the bolt extends out of the end of the housing.

The bolt may be pushed completely into me housing and rotated through 180° in order to change the hand of the latch. A slot may be provided in the face of the bolt for receiving a tool, for example, a screwdriver blade, which may be used in assisting to change the hand of the latch.

Typicallythe follower, multiplier, flexible element andbolt are injection moulded in plastics. The latchhousingispreferablydiecastinzinc. Alternatively, thehousingmaybealsoinjectionmoulded in plastics.

The inventionwillnowbe describedbywayofexample onlywithreference to the accompanying drawings in which; Fig 1 shows a side view of a latch according to the invention; Fig 2 shows a plan view from above of the latch as shown in Fig 1 ; Fig 3 is an end view of the latch of Figs 1 and 2, showing the bolt; Fig 4 is a diagrammatical cross sectional view through the latch as shown in Figs 1 and 2, with the latch in a closed position; Fig 5 is a diagrammatical cross sectional view through the latch as shown in Figs 1 and 2, with the latch in an open position; Fig 6 is an end view of a latch incorporating a second embodiment of bolt; Fig 7 is a side view of an alternative embodiment of multiplier and inelastic flexible element for use in a latch in accordance with the invention; and Fig 8 is a side view of a further embodiment of a latch.

Referring firstly to Figs 1 and 2, a door latch is indicated generally at 10. The latch 10 includes a bolt 12 which is housed in, and extends from one end of a latch housing 14 through an aperture 15.

The latch housing 14 is made in two parts 16,18, shown in Fig 2. The parts 16,18 are held together at one end by a screw 20, see Fig 1, and at the other end by a circular ferrule 22. The ferrule 22 is internally threaded and engages with a male thread provided at the end of the parts 16,18. As seen in Fig 3, the ferrule 22 is open ended, which allows the bolt 12 to pass through the ferrule. The ferrule 22 is of a larger external diameter than the housing 14, creating a stepped diameter, in the manner of a flange, at the end of the latch 10.

The outside of the housing 14 is generally cylindrical, and is designed to fit in a circular bore for ease offittingto a door (notshown). Typicallytheborewouldbe 1 inch (approximately25mm) in diameter for a standard size domestic door latch. A circular counter bore is also provided to accommodate the ferrule 22 in the edge ofthe door. In an alternative and preferred embodiment of a latch 100, shown in Fig 8, an alternative circular ferrule 90 has the same external diameter as the latch housing 14, to which it is fitted. This negates the need for a counter bore, when fitting the latch 100 in the edge of a door. The latch 100 can simply be pushed into a plane bore.

Referring now to Fig 4, a follower 24 has a spring arm 26 and an actuating arm 28 extending from opposite sides of a central hub 30. The hub 30 is mounted for rotational movement in circular apertures provided in either side of the latch housing 14. One of the circular apertures is indicated at 32 in Fig 1. A square aperture 34 is provided through the follower 24 in axial alignment with the hub 30 for receiving a square section latch driving spindle of a door handle (not shown) in conventional manner.

The follower 24 is mounted with the spring arm 26 located at the left hand end of the latch housing 14 as viewed, that is, at the closed end of the housing. Rotational movement of the follower 24 in the clockwise direction as viewed, is limited by engagement of the spring arm 26 against an upper insidewall 38 ofthe housing 14. A handle return spring 36 is located in a cavity40, which acts between the spring arm 26 and a lower inside wall 39 of the housing 14. The spring 3 6 biases the follower24 towards the limiting position shown, which corresponds to the rest position of the door handle for operating the door latch 10. A wedge (not shown) may be inserted between the spring 36 and the lower inside wall 39 ofthe housing 14 with the thin end ofthe wedge positionedpointing away from the hub 3 0 of the follower 24. The wedge tilts the central axis of the spring 3 6 allowing even compressionofthe springbetweentheuppersurface ofthewedge andthe spring arm 26.

Amultiplier42 is mounted approximatelyinthemiddle ofthe housing 14 forrotational movement about a pivot 44. A guide pin 46 is mounted on the actuating arm 28 ofthe follower 24, which cams against a pin guide surface 48 ofthe multiplier 42. The pin guide surface 48 is shaped as an evolute curve for a smooth camming action, but the pin guide surface 48 maybe straight (not

shown). The outside edge 47 ofthe multiplier 42 positioned adjacent the guide pin surface 48 is shaped as an involute curve, but also maybe straight (not shown). The relative movement of the guide pin 46 and multiplier 42, and the purpose of the involute outside edge 47 are described further below with reference to Fig 5.

The multiplier 42 is connected to the bolt 12 by means of an inelastic flexible element 50. One end ofthe element 50 is provided with aball or circular member 56 which is received in a socket 58 in the bolt 12. The other end of the element 50 is formed with an integral dovetail 52 which is received in a dovetail slot 54 in the multiplier 42 to form a dovetail joint. The ball or circular member 56 is located in the socket 58 during assembly of the joint as a snap fit.

A circular recess 60 is provided in the end of the bolt 12, which is concentric with and extends into the socket 58. One end of a coil spring 62, for biasing the bolt outwards of the housing 14, is located in the recess 60, and the other end ofthe spring 62 bears against an internal wall 64 of the housing 14. The inelastic flexible element 50 extends longitudinally within the spring 62.

The end of the bolt 12 which extends from the housing 14 is provided with upper and lower flats 66,68, also shown in Fig 3. The flats 66,68 are guided by correspondingly shaped flats 70,72 provided in the aperture 15, and prevent rotation ofthe bolt 12 relative to the latch housing 14.

Angled steps 74,76 formed between the flats 66,68 ofthe bolt 12 and the cylindrical part ofthe bolt 12 located in the housing 14, act as stops which abut the end ofthe housing 14 and limit the movement of the bolt 12 outwards of the housing.

As can be seen from Figs 2 and 3, the end ofthe bolt 12 is handed in conventional manner, one side 78 ofthe bolt being sloped for closing engagement with a keeper (not shown), and the other side 80 of the bolt being cut to be received and retained by a keeper. In orderto change the hand of the bolt 12 relative to the latch housing 14, the bolt 12 is pushed completely into the housing against the bias of the spring 62 and then rotated through 180°. When the bolt 12 is released, the spring 62 urges the bolt 12 back out of the housing with the flat 68 being guided by the flat 70 ofthe aperture 15, and the flat 66 being guided by the flat 72 of the aperture 15.

In a preferred embodiment of the bolt 12, a slot 84, shown in Fig 6, is provided in the face or side 78 of the bolt which is sloped for closing engagement with the keeper (not shown). The slot may receive a tool, for example, a screwdriver blade, which maybe used to assist in changing the hand of the latch.

The follower 24, multiplier 42, inelastic flexible element 50 and bolt 12 are preferably injection moulded in plastics. The parts of the housing 16,18 are preferably die cast in zinc. Alternatively, the parts of the housing 16,18 may also be injection moulded in plastics.

The operation of the door latch 10 will now be described with reference also to Fig 5. The latch 10 is shown in the closed position in Fig 4, that is, with the end of the bolt 12 extending from the housing 14 in its limited position. The handle return spring 3 6 is fully extended and the follower 24 is in its rest position. The square aperture 34 in the follower 24 is aligned such that a conventional handle (not shown) connected to the latch 10 is in the rest position, that is, with the handle horizontal or substantially so. The guide pin 46 is located at one end of the pin guide surface 48 and is cradled in a hook 82 of the multiplier 42.

As the door handle is depressed in order to open the door, the follower 24 is driven anticlockwise, as viewed in the direction of arrow A, about the hub 30, against the bias of the handle return spring 3 6. The guide pin 46 ofthe actuating arm 28 cams against the pin guide surface 48 of the multiplier 42, causing the multiplier to rotate anticlockwise, as viewed, about the pivot 44. The rotational movement of the follower 24 is limited to 20°, bythe engagement ofthe actuating arm 28 with the upper inside wall 38 of the housing 14, indicated by arrow B in Fig 4. However, the action ofthe guide pin 46 on the pin guide surface 48 amplifies the rotational movement ofthe follower 24, causing the multiplier 42 to rotate through at least 60°. The evolute curve ofthe multiplier 42 has the effect of smoothing the camming action, and of amplifying the rotational movement of the multiplier 42 even further than if the pin guide surface 48 were straight (not shown).

The rotation ofthe multiplier 42 causes the inelastic flexible element 5 0 to wrap around the outside edge 47 of me multiplier 42, and pulls the bolt 12 into the housing 14 against the bias ofthe spring

62. The rotational movement ofthe multiplier 42 is thereby converted to rectilinear movement of the bolt 12, indicated by arrow C. The outside edge 47 of the multiplier 42 is shaped as an involute curve in order to maximise the amount of rectilinear movement available for the amount of rotational movement of the multiplier 42.

The door latch 10 can be seen with the follower 24 and multiplier 42 at the limit of their rotational movement in Fig 5, the guide pin 46 having cammed along the pin guide surface 48, and the inelastic flexible element 50 having wrapped around the involute curve 47 of the multiplier 42. Both the handle return spring 3 6 and spring 62 for biasing the bolt 12 outwards of the housing 14 are compressed. When the handle is released, the spring 62 forces the bolt 12 out of the housing 14, which pulls the inelastic flexible element 50 in the opposite direction away from the multiplier and causing the multiplier to rotate clockwise, as viewed, back to the rest position. The handle return spring 36 returns the follower 24 and hence the handle, back to their rest positions.

When the bolt 12 is pushed into the housing 14, either to change the hand of the bolt, or when the bolt engages akeeper as the door is slammed shut, the inelastic flexible element 50 simply bends to accommodate the movement. As the movement of the follower 24 is limitedto 20° of rotation, the door handle need only be moved through an arc of 20° in order to release the bolt 12 and open the door. Therefore, the door latch 10 of me invention significantly reduces the handle movement required in opening a conventional door latch, for easier operation.

An alternative embodiment of multiplier 142 and inelastic flexible element 150 is shown inFig 7.

The end of the inelastic flexible element 150 is provided with a substantially circular enlargement 88, which is received and retained in a correspondingly shaped recess 92 in the multiplier 142. The circular enlargement 88 is a clearance fit in the recess 92, and hence is able to rotate to a limited degree to align itself to the direction of any applied forces. This substantiallyreduces the stresses present at the position where the circular enlargement 88 necks into the length of the inelastic flexible element 150, and consequently improves the durability ofthe inelastic flexible element 150 in use.