GB662408A - Improvements relating to power transmission gearing - Google Patents

Abstract

662,408. Change-speed gearing; clutches. NAPIER & SON, Ltd., D. April 27, 1950 [Nov. 4, 1949], No. 28324/49. Class 80 (ii) Power transmission gearing between an engine-driven shaft 11, Fig. 2, and a marine propeller shaft comprises an auxiliary forward train including gears 23, 32 and a friction clutch 34, and a main forward train including gears 13, 14 and an over-running dog clutch 28, 29, the two trains being in parallel with the transmission ratio of the main train slightly lower than that of the auxiliary train so that the dog clutch 28, 29 automatically takes over the drive as the friction clutch disengages, the latter being engaged at starting by moving a control lever 86 to the forward position Z but being automatically disengaged when a predetermined engine speed is exceeded. A reverse train including a gear 24 and a friction clutch 37 is also provided. The dogs 28 are formed on a sleeve 26 threaded on a quick-pitch screw 27 on the shaft 11 and carrying shoes 30 held in frictional contact with the gear 13 by springs. When disengaged, the driven disc of each friction clutch is held central by a plunger 60, Fig. 4, engaging a recess in the disc under the influence of a spring 63 and of centrifugal force. The friction clutches are selectively engaged by pressure oil supplied through the hollow shaft 11 under the control of an axially-movable valve tube 46 to passages 44 leading to an inner annular chamber 42, which leaks into an outer annular chamber 43. When the supply of oil is stopped, chamber 43 is vented via port 71 and an escape valve 48, Fig. 5, and oil can also escape past the discs. Valve 48 is normally held open by a spring 64, but, during engagement of the clutch, is closed by pressure oil supplied to port 65 through passages 53 under the control of valve tube 46, and oil from passages 53 now has access to port 71 so as to supplement the supply to chamber 43. When the pressure in chamber 42 has built up sufficiently, valves 74 open to increase the flow from chamber 42 to chamber 43. By this construction, the drive is taken up smoothly. The open end of the tube 46 carries a piston 83 movable in a cylinder 84 carried by the lever 86, the piston moving to the right-hand end of the cylinder when the oil is under pressure and being moved by a spring 85 to the left-hand end when the oil pressure is relieved. The supply of oil to the tube 46 is controlled by a valve 94 operated by an engine-driven governor 95 so that the valve 94 is open only below a predetermined engine speed. The valve 94 is, however, held open at all speeds when the lever 86 is in reverse position X by means of an arm 98. Interlocking means 100 ensure that the lever 86 cannot be moved except when the engine control 99 is in idling position. With the lever 86 in neutral position Y, as shown, with engine stopped, piston 83 is at the left of cylinder 84 and the end 82 of tube 46 projects beyond the end of shaft 11 to hold the dogs 28, 29 apart. If the engine is now started, piston 83 moves to the right of the cylinder 84, but the end 82 still projects to hold the dogs apart. On moving lever 86 to forward position Z, it moves cylinder 84 and tube 46 to the left and friction clutch 34 engages. When the predetermined engine speed is exceeded, valve 94 cuts off the supply of oil and the clutch 34 exhausts, allowing it gradually to disengage. Piston 83 also moves to the left in cylinder 84, retracting end 82 into shaft 11, so allowing the dogs to engage as shaft 11 begins to overtake pinion 13. When lever 86 is in the reverse position X, the end 82 holds the dogs apart at all times.