Principles of naval engineering - Historic Naval Ships Association

Chapter 22. -DIESEL AND GASOLINE ENGINESFRICTION BLOCKSFORWAFD CLUTCHSHIFTER ARMCONTROLLEVER\NEUTRAL PORTS V)FORWARD^'ROTARY AIRJOINTSPRINGCARBON CYLINDERFORmRD PORTSAIR]SEALSFOUR-WAY VALVEEMERGENCYSHAFTAIRFITTINGORIFICECHECKAIRVALVEREVERSE PASSAGEREVERSE CLUTCHFigure 22-39.— Airflex clutches and control valves.75.257eliminates the need for a mechanical connectionbetween the engine and the reduction gears.Couplings of this type operate with a minimumof slippage.Some slippage is necessary for operation ofthe hydraulic coupling, since torque is transmittedbecause of the principle of relative motionbetween the two rotors. The power lossresulting from the small amount of slippage istransformed into heat which is absorbed by theoil in the system.Compared with mechanical clutches, hydraulicclutches have a number of advantages. Thereis no mechanical connection between the drivingand driven elements of the hydraulic coupling.Power is transmitted through the coupling veryefficiently (97 percent) without transmittingtorsional vibrations, or load shocks, from theengine to the reduction gears. This protects theengine, the gears, and the shafting from suddenloads which may occur as a result of pistonseizure or fouling of the propeller. The poweris transmitted entirely by the circulation of adriving fluid (oil) between radial passages in apair of rotors. In addition, the assembly of thehydraulic coupling will absorb or allow forslight misalignment.The two rotors and the oil-sealing cover ofa typical hydraulic coupling are shown in figure22-41. The primary rotor (impeller) is attachedto the engine crankshaft. The secondary rotor(runner) is attached to the reduction gear pinionshaft. The cover is bolted to the secondaryrotor and surrounds the primary rotor. Eachrotor is shaped like a half-doughnut with radialpartitions. A shallow trough is welded into thepartitions around the inner surface of the rotor.The radial passages tunnel under this trough(as indicated by the white arrows in fig. 22-41).589