Chapter 22. -DIESEL AND GASOLINE ENGINES 



FORWAFD CLUTCH 



FRICTION BLOCKS 



SHIFTER ARM 



CONTROL LEVER 



\ 



] 

 NEUTRAL PORTS V) 



FORWARD^' 



ROTARY AIR 

 JOINT 



SPRING 



CARBON CYLINDER 



FORmRD PORTS 



AIR SEALS 



FOUR-WAY VALVE SHAFT 



EMERGENCY FITTING 



AIR ORIFICE 



AIR CHECK 



VALVE 



REVERSE CLUTCH 

 REVERSE PASSAGE 



75.257 



Figure 22-39.— Airflex clutches and control valves. 



eliminates the need for a mechanical connection 

 between the engine and the reduction gears. 

 Couplings of this type operate with a minimum 

 of slippage. 



Some slippage is necessary for operation of 

 the hydraulic coupling, since torque is trans- 

 mitted because of the principle of relative mo- 

 tion between the two rotors. The power loss 

 resulting from the small amount of slippage is 

 transformed into heat which is absorbed by the 

 oil in the system. 



Compared with mechanical clutches, hydrau- 

 lic clutches have a number of advantages. There 

 is no mechanical connection between the driving 

 and driven elements of the hydraulic coupling. 

 Power is transmitted through the coupling very 

 efficiently (97 percent) without transmitting 

 torsional vibrations, or load shocks, from the 

 engine to the reduction gears. This protects the 

 engine, the gears, and the shafting from sudden 



loads which may occur as a result of piston 

 seizure or fouling of the propeller. The power 

 is transmitted entirely by the circulation of a 

 driving fluid (oil) between radial passages in a 

 pair of rotors. In addition, the assembly of the 

 hydraulic coupling will absorb or allow for 

 slight misalignment. 



The two rotors and the oil-sealing cover of 

 a typical hydraulic coupling are shown in figure 

 22-41. The primary rotor (impeller) is attached 

 to the engine crankshaft. The secondary rotor 

 (runner) is attached to the reduction gear pinion 

 shaft. The cover is bolted to the secondary 

 rotor and surrounds the primary rotor. Each 

 rotor is shaped like a half-doughnut with radial 

 partitions. A shallow trough is welded into the 

 partitions 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 



