Patent GB-914578-A (GB)
Title: Improvements relating to marine forward-reverse gear propulsion systems
IPC: B63H23/08
Filed: 1960-05-23
Abstract: 914,578. Reverse gear control; positive clutches. SINCLAIR, H. May 17, 1961 [May 23, 1960], No. 18172/60. Class 80 (2). A marine forward-reverse gear in which positive clutches are provided for selectively driving a ship's propeller in ahead or astern sense by a prime mover intended for unidirectional rotation comprises an eddy current brake and a friction brake provided for use in reducing the speed of a shaft coupled to drive the propeller, the eddy current brake being operable over at least the upper part of the speed range of the propeller and the friction brake being operable only over a lower part of the speed range of the propeller and for holding the propeller shaft system stationary. Engagement of the forward and reverse establishing clutches is effected when the propeller is at rest. In one form, an input shaft 1, which may be connected directly to a steam or gas turbine, or to a Diesel engine through an hydraulic turbo coupling, carries a gear A meshing a gear B which may be connected through a forward clutch CL2 to a shaft 2 carrying a gear F meshing an output gear D fast on a driven shaft 3, the gear B also meshing a gear C which can be connected through a reverse clutch CL4 to a shaft 4 fast upon which is a gear R meshing the output gear D. Two electro-dynamic brakes EBR2, EBR4 are provided on the lay shafts 2, 4, and a fluid-pressure actuated spot-type disc brake BR3 is provided on the driven shaft 3. The forward and reverse clutches CL2, CL4 are both of the Legge type, each comprising a sleeve 7 mounted upon helical splines upon the associated lay-shaft and having oppositelydirected sets of ratchet pawls 11, 11<SP>11</SP> selectively engageable with teeth 10 in a sleeve fast with the associated gear B or C, the teeth 10 also being engageable by teeth 5 on the sleeve 7. The sets of helical splines on the shafts 2, 4 are of opposite hand. Each clutch has a locking sleeve 12 splined at 14 to the intermediate sleeve 7, and having internal teeth 15 selectively engageable with teeth 17 on a sleeve 9 fast with the associated shaft 2 or 4. The locking sleeves 12 are controlled through a lever 40 biased in one direction or the other through resilient means (not shown). When it is desired to change from, e.g., ahead drive, with the clutch CL2 engaged, to reverse drive, with the teeth 10 of the clutch CL2 engaged by the teeth 5 on the intermediate sleeve 7, the engine fuel control is closed to idling position, and the control lever 40 is biased to unlock the ahead clutch CL2 and to lock the astern clutch CL4. The eddy current brakes EBR2, EBR4 are then energized to retard their shafts 2, 4, and through the gears F, R, the driven shaft 3. When the speed of the propeller shaft 3 drops below half its maximum speed, the friction brake BR3 is applied so as to bring the shaft system to rest. A baring drive BR1 is then operated to rotate the input shaft 1 backwards so that the intermediate sleeve 7 of the ahead clutch CL2 moves rightwards along its helical splines, disengaging its teeth 5, 10 and thereby unloading the locking sleeve 12 which is moved by resilient bias to its unlocked position. During this time and until the propeller shaft comes to rest, rotation of the gear shaft keeps the astern clutch CL4 disengaged. When the driven shaft 3 is at rest, and the baring drive BR1 turns the input shaft 1 backwards as described, the sleeve 7 of the ahead drive clutch CL2 moves to the right, as described, and similarly the sleeve 7 of the reverse drive clutch CL4 moves to the right. When the sleeve 7 of the astern clutch CL4 has moved far enough for full engagement, its locking sleeve 12 is moved into position to lock the astern clutch in engagement for the transmission of driving torque when the normal rotation of the input shaft 1 is resumed after releasing a clutch 38 in the baring drive BR1. The ahead clutch CL2 is then in its freewheeling or ratcheting position. The pawls 11, 11<SP>11</SP> are so constructed that they are maintained out of engagement with the teeth 10 by centrifugal force when the clutches are freewheeling. Establishment of ahead drive from reverse is effected in a similar manner. In a modified form, Fig. 2 (not shown), the two eddy current brakes EBR2, EBR4 on the shafts 2, 4 are replaced by a single eddy current brake on the input shaft 1. Specifications 493,703 and 837,776 are referred to.