Patent GB-493909-A (GB)
Title: Improvements relating to fastenings for doors
IPC: E05B63/20
Filed: 1937-03-13
Abstract: 493,909. Latch mechanism. DARBY, J. H. March 13, 1937, Nos. 7389/37, 10489/37, and 7789 /38. [Class 44] A door fastening comprises a spring-pressed bolt, an operating lever, trip mechanism for holding the bolt fully retracted when the door is open and for releasing it when the door reaches the closed position, and a safety bolt, separate from or forming part of the main bolt, which is withdrawn by the operating lever only after the lever has been moved a predetermined extent. A bolt 3, Fig. 1, has a downwardlybent tail 5 on which a spring 4 and a follower 7 act to project and retract the bolt, respectively. An arm 11, pivoted to swing horizontally, is spring pressed to engage a detent 9, carried by the arm, in a notch 10 on the bolt when the door is open, to hold the bolt in the retracted position until, on the door reaching the closed position, the arm 11 is displaced by some part of the keeper to allow the bolt to be shot by the spring 4. A curved safety bolt 13, pivoted to the casing at 16, has a tapered lower end 17 which engages either side of the apex of a spring 18 to hold the bolt 13 in its extreme positions. The bolt 13 is made to follow the movements of the main bolt 3 by a projection on the latter engaging pins 14, 14<1>, on the bolt 13, the pins being spaced apart so that the bolt 13 does not move until the bolt 3 has nearly completed its movement. In the latch shown in Fig. 2, two sliding bolts are used, the main bolt 19 being retracted by a follower 31 and the safety bolt 20 being retracted by an adjustable projection 23 on the bolt 19 which encounters an arm 24, extending laterally from the bolt 20, when the bolt 19 has been partly retracted by an anticlockwise movement of the operating handle. The arm 24 is pivoted on the bolt 20 at 25 and pressed by a leaf spring 27 into the path of the projection 23 on the bolt 19. When the handle is released a spring 44 turns the spindle 32 clockwise to its normal position and an arm 35 lifts the arm 24 out of line with the projection 23 and the bolt 20 is shot by a light spring 41. The main bolt 19 is held retracted by a pivoted lever 36, the inner end of which is pressed by a spring 40 into engagement with a stop 39 on the bolt, and is shot by a spring 28 when the projecting end of the lever 36 contacts the keeper. Other means may be provided to permit the safety bolt 20 to resume its outward position such as a lever adapted to contact a stop on the keeper to disconnect the safety bolt from the main bolt after the safety bolt has cleared the keeper. In a modification, Fig. 4, a single bolt, formed of two parts disposed in alignment, is used. The rear part 46 is held retracted when the door is open and released when the door closes by trip mechanism similar to that shown in Fig. 1. The part 46 is retracted by a follower 52 which also retracts the forward part 45 by means of a spring 65. The part 45 is prevented from inward movement until the part 46 has been partly or fully retracted by a trip mechanism, not shown, which may comprise two obtuse-angled levers pivoted to the casing above the bolt. The part 46 in its retractive movement engages the rear arm of one lever and causes the front arm of this lever to depress the rear arm of the other lever, thus disengaging its front arm from a stop on the upper edge of the part 45. On release of the operating handle the follower 52' is returned to its normal position by a spring 66 and during this movement it engages a buffer 69 mounted to slide longitudinally on the part 45. As the compression spring 68 on the buffer is stronger than the spring 65 and the spring 66 is stronger than either of them, the part 45 is returned to its projected position. During slamming of the door, the inward movement of the part 45 as it rides over the face of the keeper is absorbed by the spring 68. The latch shown in Fig. 2 may be modified by omitting the projection 23, arm 24, and arm 35, the bolt 20 being retracted by a second follower disposed on the spindle 32 at an angle to the follower 31 so that the main bolt 19 is partly retracted before the safety bolt 20 is moved. The bolt 20 returns to its projected position when the handle is released. The projection on the bolt 19 which is engaged by its follower is closer to the axis of the follower than the corresponding projection on the bolt 20 in order to give an increased leverage to overcome the pressure of the spring 28, which is stronger than the spring 41, and also to impart a quicker movement to the bolt 20. The separate followers may be replaced by a compound follower so shaped that the main bolt is completely retracted before the safety bolt is moved, further rotation of the follower retracting the safety bolt without affecting the main bolt. The latch shown in Fig. 4 may be adapted for actuation by two followers or by a compound follower, the rear part of the bolt having a strong spring and the forward part, a weaker spring. In a further modification, two bolts, one above the other, are used, the lower bolt, which has a strong spring, engaging behind a shoulder on the upper bolt, which engages the keeper under the action of a weak spring. The projections engaged by the follower, which is of curved form are so arranged that the lower bolt is moved first and retained by trip mechanism similar to that shown in Fig. 1, whilst the upper bolt is retracted after the lower bolt has been partly retracted and returns to its projected position when the handle is released. In a further modification, the safety bolt is pivoted to move in a vertical plane and is lifted by an arm on the handle spindle when the main bolt has almost reached its fully retracted position and lowered into engaging position when the handle is released. The main bolt is held retracted by a detent integral with a trip lever pivoted on the handle spindle. The keeper may have a rubber roller mounted for rotation on a vertical axis to guide the bolt noiselessly to its final position, when it is released by the trip mechanism. When both bolts engage the keeper, the safety bolt may be arranged above, below, in front of, or within the main bolt. In addition to manual operation the latches may be electrically operated by remote control.