Patent GB-1185641-A (GB)
Title: Improvements in or relating to Door Latches
Inventor: JAMES MICHAEL JOSEPH
IPC: E05C1/16
Filed: 1966-03-14
Abstract: 1,185,641. Latches. MICRO & PRECISION MOULDINGS (CHELTENHAM) Ltd. 9 March, 1967 [14 March, 1966], No. 11000/66. Heading E2A. A tubular mortise latch of the kind having a slidable slam bolt 5 mounted in a housing 1 of generally tubular form and shaped to be receivable in a bore of circular cross section, the latch being released in use by withdrawal of the bolt into the housing by turning door handles respectively mounted on opposite sides of the door and interconnected by an operating shaft, has a rotary actuating member 19 which is turned by the operating shaft and acts to withdraw the bolt into the housing and an intermediate follower member 25 which engages and pivots on a fixed abutment 13 in the housing 1, such engagement defining an effective pivot axis parallel to the rotary axis of the actuating member, offset vertically with respect to the bolt axis when the latch is mounted with that axis horizontal, and which is engaged and turned by the actuating member to release the latch, the follower member in turn engaging the bolt 5 to produce axial withdrawal of the latter into the housing and the arrangement being such that the angular movement of the follower member is greater than that of the actuating member and a latch spring 18 to urge the bolt to a latching position. In the construction shown there are two abutments 13 disposed one on each side of the housing and with which projecting side limbs 27 of the follower member engage; each abutment has a generally rectangular recess (not shown) with radiused corners disposed symmetrically above and below the bolt axis, and in either of which the follower member side limbs can engage and pivot, depending on the direction in which it is turned by the actuating member, the arrangement enabling either direction of handle movement, in use, to effect latch release. The follower member has a projecting central web which passes with clearance between the abutments 13, the web having upwardly and downwardly projecting ears 29 which respectively engage longitudinal slots in side limbs 17 of the bolt to effect latch release. The side limbs during bolt withdrawal slide above and below the fixed abutments 13. In the protruding position of the bolt the bottom faces of the recesses in the abutments are engaged by side faces of the side limbs of the follower member to limit the protrusion of the bolt, the bolt being biased by the spring 18 to the protruding latching position, the spring acting between the bolt and an abutment 14 in the housing. The actuating member has a peg-like section which engages open ended slots 36 formed in inward projections of both side limbs of the follower member so that rotation of the actuating member also rotates the follower member. The housing has a separate end portion 6 which closes the inner end of the latter and which is fitted after the actuating member and the follower member have been inserted from that end of the housing and the portion 6 contains an auxiliary return spring 43 which acts directly on an axially slidable plunger 44 formed with a concave recess engaged by an inwardly projecting lobe 46 of the actuating member; side faces of the lobe engage the housing to limit handle movement. The bolt limbs 17 are moulded with tooth-like projections 50 and the central follower web 26 is moulded with corresponding recesses 52 for engagement by the projections 50 when the bolt is pushed fully home with the follower member 25 in the central resting position, this enables the latch to be fitted to the door by a manufacturer and supplied with the bolt fully retracted so that it is not liable to accidental damage during transport and fitting of the door. The bolt limbs are each provided with an extension 39 with an end formation 40, the formations 40 being received in upper and lower slots 42 in the actuating member 19, which slots extend into the shaft receiving aperture 20 so that the formations 40 enter the aperture 20 and engage the shaft resiliently when the latter is fitted, this resilient engagement provides some assistance in centering the shaft to define the handle resting position. The shaft and handle construction can be such that the shaft is axially displaceable from one side of the door to a locking position in which the opposite side door handle can turn freely without turning the shaft, the shaft in such case being provided with a side notch which in the locking position is engaged by the formations 40 to retain it in such a position, release being effected by turning the other handle.