GB866046A - Clutch mechanism for connecting a rotary driving member with a rotary driven member - Google Patents

Abstract

866,046. Ratchet clutches. UNITED AIRCRAFT CORPORATION. March 25, 1959 [April 9, 1958], No. 10329/59. Class 80 (2). [Also in Group XXVII] A ratchet clutch for use in a starter for an aircraft engine is maintained engaged during starting by centrifugal balls rotated by the driving shaft and is subsequently maintained disengaged by centrifugal balls rotated by the driven shaft. An input part 74 of the clutch is connected by spiral splines 78 to a member 68 driven through reduction gearing by a gas turbine starter rotor, and has ratchet teeth 80 engageable with teeth 82 on a driven clutch part 84 which drives the aircraft engine. The clutch is maintained engaged by balls 94 driven by fins 104 on a supporting ring 102 rotating with the driving member 68, the balls co-operating with a cam surface 97 formed on the input clutch part 74. A second set of balls 96 is positioned between fins 114 of a support ring 106 rotating with the driven part of the clutch but axially slidable relative thereto; the balls co-operate with a cam surface 108 on the part 84, outward movement of the balls moving the supporting ring 106 to the left, the ring being connected by a bearing to clutch part 74 and so disengaging it. A light spring 120 engages the clutch when the driving and driven parts are stationary; upon driving the starter turbine both clutch parts are rotated and the balls 94, 96 start to move radially outwardly. The balls 94 are located further from the axis than the balls 96 and so exert a greater axial force on the clutch part 74 than the balls 96 to maintain it engaged. When the aircraft engine starts, flow of gases to the starter is interrupted, and the ratchet teeth 80, 82 disengage. As the part 74 moves out of engagement, the balls 94 are forced inwardly and balls 96 move outwardly, and, due to the greater speed of rotation of the clutch part 84, the balls 96 exert a greater axial force on the clutch part 74 than the balls 94 so that the clutch is positively maintained disengaged. The clutch will also engage during a running start, i.e. when operation of the engine starter is initiated with the aircraft engine rotating at a speed below its starting speed. Under these conditions the clutch parts 74, 84 are disengaged, with balls 96 being rotated and balls 94 stationary. When the starter turbine commences to rotate the balls 94 begin to revolve and are urged outwardly to the position shown in which the balls 94, 96 are substantially equi-distant from the axis. As the starter accelerates the force due to the balls 94 and spring 120 becomes sufficient to engage the clutch. When the aircraft engage is stopped, the clutch is re-engaged by the spring 120, and in order to minimize ratcheting and ensure that re-engagement only occurs at a low engine speed, cam surface 108 is formed with an outer part 112 at an angle of 16 degrees to a radial plane and inner portion 110 at an angle of 45 degrees, cam surface 97 having outer and inner parts 100, 98 at angles of 45 degrees and 16 degrees respectively.