GB514573A - Improvements in or relating to ratchet reduction gearing - Google Patents

Abstract

514,573. Driving mechanism for electric clocks. AGAR, M. F., and MAW, T. F May 10, 1938, No. 13996. [Class 139] [Also in Group XXIV] In ratchet gearing wherein a pawl is moved by a pawl a tooth at a time for each revolution of a driving shaft, means are provided for moving the pivoted end of the pawl in a substantially elliptical path while the free end of said pawl bears constantly on the periphery of the ratchet wheel, so that the pawl tooth moves at a very slow speed at the moment of engagement with a tooth of the ratchet wheel. A rachet wheel 2 is loosely mounted on a driving shaft 1 carrying a cam 3 embraced by a hooklike portion 4 of a lever 5 having a knife-edge pivot 6, 7 with a link 8 pivoted to a rigid support 9 by a knife-edge pivot 11, 12. Pivoted in a recess 13 of lever 5 is a pawl 14 held in the recess by a spring 15 attached to link 8 or to the frame of the mechanism. The other end of the pawl is forked and passes around and is guided by an extension 17 of link 8. The spring 15 holds one limb in contact with the periphery of the wheel 2, the other limb being supported and guided by a surface 19 on the support 9. The upper end of lever 5 at the recess 13 moves in a substantially elliptical path b which causes the pawl tooth 18 to move at a very slow speed at the moment of engagement with the ratchet wheel. The forked end of the pawl rolls over the periphery of the wheel 2. As applied to a synchronous electric clock the armature 21, Fig. 2, of the electric motor 20 is mounted on the shaft 1 which carries the cam 3 embraced by the lever 4. Fast on the ratchet wheel 2 is a further cam 3a the pawl actuated by which drives the ratchet wheel 2a and this drives the minute hand through a sleeve 27, the usual reduction gear being employed for the hour hand. A strip 24 prevents movement of wheel 2 between impulses of the pawl tooth, and a light spring 33 prevents backward movement of the ratchet wheels. In a modification, Fig. 3, the knife-edge pivots are omitted and the lever 5 is secured to a member 40 connected at 43 to a support 41, in the form of a clamp, by a leaf spring 42. To the other end of member 40 is rigidly clamped the pawl 44 in the form of a leaf spring. An extension 5a extending downwardly over the wheel 2 prevents lateral movement.