Patent GB-837776-A (GB)
Title: Improvements relating to marine forward-reverse gear propulsion systems
IPC: F16H3/14
Filed: 1957-06-14
Abstract: 837,776. Reverse gear control; positive clutches. SINCLAIR, H. June 13, 1958 [June 14, 1957], No. 18922/57. Class 80 (2). Reverse gearing for ships comprises a driving shaft 1, Fig. 1, carrying a gear A meshing a gear B connected through a forward drive positive clutch CL2 to a shaft 2 carrying a gear F meshing a gear D fast upon a driven shaft 3 carrying a propeller, the gear B meshing a gear C connected through a reverse drive positive clutch CL4 to a shaft 4 fast with a gear R also meshing the output gear D, the clutches CL2, CL4 being of the Legge type having a member constrained to move helically during engagement/disengagement, establishment of either forward or reverse being effected by first unlocking the already engaged clutch, applying a brake BR3 to station the driven shaft 3 and then turning the input shaft 1 backwards. The engaged clutch CL2 or CL4 is normally locked in engagement by operation of a control lever 40. The shaft 1 is either driven from an engine through a fluid coupling of the scoop type or, if the engine is a gas turbine, is connected directly thereto. To change over from, e.g. ahead drive to astern drive, the engine is first throttled down, and the control lever 40 operated to unlock the forward drive clutch CL2. The output shaft brake BR3 is applied to bring the shaft system to rest, and disengage the clutch CL2. When the output shaft 3 is at rest, the input shaft 1 is rotated backwardly by means BR1 (described below) and engages both the forward and reverse drive clutches CL2, CL4. The reverse clutch CL4 is locked in engagement by the lever 40, ready to rotate the output shaft 3 in the reverse direction when the engine takes up drive, the forward clutch CL2 then unscrewing to the disengaged position. Positive clutches.-In one form, the gear B, Fig. 2, is provided with dog teeth 5 engageable by teeth 10 upon an intermediate sleeve 7 slidable along helical splines 6 upon the shaft 2, the intermediate sleeve 7 also carrying pawls 11 for engagement with the teeth 5. A locking sleeve 12 is axially slidable upon a toothed sleeve 9 secured to the shaft 2 and having teeth 15, 16 engageable with teeth 17, 18 on the sleeve 9. The reverse clutch CL4 is of similar construction, but with the helical splines 6, &c. arranged to operate in the opposite direction of rotation. When the direction of relative rotation between the gear B and the shaft 8 is such that the pawls 11 pick up the dog teeth 5, the intermediate member 7 is drawn helically along the splines 6 to engage the clutch teeth 10, 5. The locking sleeve 12 can then be slidden to engage its teeth 15, 16 with the teeth 17, 18 fast with the shaft sleeve 9. The teeth 5 are of such a length that the teeth 10 can slide further rightwards, beyond their normal fully-engaged position shown at x, until the intermediate member 7 abuts a stop 8 upon the shaft 2. By this means, reverse rotation of the input shaft 1 to engage the disengaged clutch, e.g. the reverse drive clutch CL4, causes the teeth 10 of the forward drive clutch to be slidden rightwards beyond their normal engaged position, while still remaining in engagement with the teeth 5. When the input shaft 1 is again rotated in its normal direction, the teeth 10 are then slidden leftwards by the unscrewing of the intermediate member 7 on the helical splines 6 to the disengaged position shown in Fig. 2. The change from reverse to forward drive is similarly effected. The tails of the pawls 11 of the reverse clutch CL4 are extended so that centrifugal force acting thereon pivots the pawls to the disengaged position and prevents ratcheting when the ship is driven ahead. In modified form of clutch, the teeth 5, Fig. 4, are of lesser axial width, and an extra ring of pawls 11<SP>11</SP> are provided, having their noses pointing in the opposite direction to the noses of the pawls 11. On engagement of the disengaged clutch, the teeth 10 on the intermediate sleeve 7 are slidden rightwards out of engagement with the teeth 5, but the pawls 11<SP>1</SP> then engage the dog teeth 5 so that when the normal direction of rotation of the input shaft 1 is resumed, these secondary pawls can initiate the unscrewing movement of the intermediate sleeve 7 to first engage the teeth 5, 10, in order that the intermediate sleeve 7 can then be screwed leftwards to the fully disengaged position shown. In a further modification of this form, the pawls 11<SP>11</SP> are omitted, the intermediate sleeve 7 instead being biased leftwards to reengage the teeth 5, 10 by a light spring. In the form shown in Fig. 1, reverse rotation by the means BR1 of the input shaft 1, which is assumed to be driven by a gas turbine, is effected by engagement of a clutch 38 driven from the associated turbine apparatus through a worm and worm wheel 41, 39. Alternatively, a fluid pressure servomotor (not shown) may operate through links 29, 28, Fig. 3, to turn a cam 27 and engage friction shoes 25 with a drum 24 secured to the shaft 1, the shoes pivoting upon a spider 36 against the bias of disengaging springs 26. Continued movement of the links 29, 28, &c. then turns the spider 36 and the friction shoes 25 against the bias of a spring 33 and thereby rotates the drum 24 and the input shaft 1 fast therewith backwards. Specifications 493,703, 512,517, 773,545, 798,850 and 813,043 are referred to.