Patent GB-881744-A (GB)
Title: Latches for doors
IPC: E05B55/12
Filed: 1959-04-02
Abstract: 881,744. Latch fastenings. PARKES & SONS Ltd., JOSIAH, BUTTER, F. J., and ORDIDGE, E. F. March 30, 1960 [April 2, 1959], No. 11214/59. Class 44. In a latch for doors of the type wherein a spring loaded latch bolt has on that side remote from its bevelled striking face a spring loaded auxiliary slide which is moved in with the latch bolt when the latter is operated by either of two followers 13, 19, or is pressed back by the striking plate or staple 35 but which is prevented by the latter from moving forward with the latch bolt when the bolt head 10 enters a recess in the striking plate or staple and in which when the door is opened the auxiliary slide holds a dog out of the path of an abutment on the latch bolt but when the door is closed allows the dog to move into position to the rear of said abutment so as to secure the bolt in the shot out position against backward pressure on the bolt head and in which the follower 13 is operable by a knob from the inside of the door and the follower 19 is operable by a key from the outside of the door through a rotary plug of a cylinder lock, the follower 13 having the form of a crank disc with a cam surface for displacing the dog from its locking out position and with a crank pin 15 which bears directly upon a forwardly presented face on the bolt lath 11 to withdraw the latch bolt after the dog has been displaced during the initial part of the rotation of this follower in the bolt withdrawing direction, whilst the follower 19 has a radial abutment arm 18 which co-operates with the crank' pin 15 to cause the latter to withdraw the bolt when the follower 19 is turned by the key in the appropriate direction, an additional dog is provided which co-operates with the auxiliary slide only and which is adapted whenever the door is open and the slide is clear of the striking plate or staple to prevent the full reverse rotation of the follower 19 into a position in which it can lock the follower 13 against bolt withdrawal and when the door is closed not to interfere with rotation of the follower 19 in both directions. As shown the latch bolt is biased by a spring arm 12. The bolt head is formed with a longitudinal recess of dovetail form in cross-section which constitutes a housing and guide way for the leading portion 27 of the auxiliary slide which is normally maintained in its extended position by a second spring arm 31. The first dog is pivoted at 37 to the latch case 21 and is in the form of a bellcrank lever; its vertical arm 38 is loaded rearwardly by a spring arm 39 and its other arm 33 is engageable with the rear face of the bolt head which forms the abutment. The auxiliary slide is formed with a rearward portion 28 which extends over a centre rib of the bolt lath 11 and this portion 28, when the auxiliary slide is in its forward position, maintains the arm 33 of the dog out of engagement with the bolt head but when the auxiliary slide is retracted, when the door is closed, by engagement with an abutment 36 on the striking plate or staple allows the arm 33 to engage behind the bolt head. The follower 13 has a cam 40 which when the follower is turned in a bolt-withdrawing direction first operates the first dog by moving the vertical arm 38 forwardly, thus pivoting the arm 33 upwardly and away from the rear of the bolt head, to allow the bolt to be withdrawn. The second dog is pivoted at 41 to the latch case 21 and is loaded either by gravity or, as shown, by a spring 42 so that one of its arms 43 is urged into engagement with the portion 28 of the auxiliary slide. The arrangement is such that when the auxiliary slide is held in its rearmost position or nearly so by engagement with the striking plate or staple the other arm 44 of the dog dogs not interfere with rotation of the follower 19. When, however, the auxiliary slide is in its extended position the second dog can pivot so that its arm 44 projects into the path of the radial abutment arm 18 of the follower 19 and prevents the follower being turned into a position in which its arm 18 engages forwardly against the pin 15 of the follower 13 in which position it would lock the follower 13 against withdrawal by the knob when the key is removed. The arm 43 of the second dog has a ramp 45 which co-operates with the portion 28 of the auxiliary slide to displace the dog to its ineffective position when the slide is moved rearwardly. Alternatively the rear end portion 28 of the slide may be formed with the ramp for displacing the second dog.