PRINCIPLES OF NAVAL ENGINEERING 



drive shaft, which carries the double helical 

 forward pinion at the after end of the gear box. 

 The forward pinion is in constant mesh with the 

 double helical main gear, which is keyed on the 

 propeller shaft. By following through the gear 

 train, you can see that, for ahead motion, the 

 propeller rotates in a direction opposite to the 

 engine's rotation. 



The parts of the airflex clutch which give 

 the propeller astern rotation are illustrated in 

 the lower view of figure 22-32. The reverse 

 clutch is inflated to engage the reverse drum, 

 which is then driven by the engine. The reverse 

 drum is keyed to the short reverse shaft, which 

 surrounds the forward drive shaft. A large 

 reverse step-up pinion transmits the motion to 

 the large reverse step-up gear on the upper 

 shaft. The upper shaft rotation is opposite to 

 the engine's rotation. The main reverse pinion 

 on the upper shaft is in constant mesh with the 

 main gear. By tracing through the gear train, 

 it may be seen that, for reverse rotation, the 

 propeller rotates in the same direction as the 

 engine. 



The diameter of the main gear of the airflex 

 clutch is approximately 2 1/2 times as great 

 as that of the forward and reverse pinions. Thus, 

 there is a speed reduction of 2 1/2 to 1 from 

 either pinion to the propeller shaft. 



Since the forward and main reverse pinions 

 are in constant mesh with the main gear, the 

 set that is not clutched in will rotate as idlers 

 driven from the main gear. The idling gears 

 rotate in a direction opposite to their rotation 

 when carrying the load. For example, with the 

 forward clutch engaged, the main reverse pinion 

 rotates in a direction opposite to its rotation for 

 astern motion (note the dotted arrow in the upper 

 view of figure 22-32. Since the drums rotate in 

 opposite directions, a control mechanism is in- 

 stalled to prevent the engagement of both clutches 

 simultaneously. 



The airflex clutch is controlled by an oper- 

 ating lever which works the air control housing, 

 located at the after end of the forward pinion 

 shaft. The control mechanism, shown with the 

 airflex clutches in figure 22-39, directs the high 

 pressure air into the proper paths to inflate 

 the clutch glands (tires). The air shaft, which 

 connects the control mechanism to the clutches, 

 passes through the forward drive shaft. 



The supply air enters the control housing 

 through the air check valve and must pass through 



the small air orifice. The purpose of the re- 

 stricted orifice is to delay the inflation of the 

 clutch to be engaged, when shifting from one 

 direction of rotation to the other. The delay is 

 necessary to allow the other clutch to be fully 

 deflated and out of contact with its drum before 

 the inflating clutch can make contact with its 

 drum. 



The supply air goes to the rotary air joint 

 in which a hollow carbon cylinder is held to 

 the valve shaft by spring tension. This pre- 

 vents leakage between the stationary carbon 

 seal and the rotating air valve shaft. The air 

 goes from the rotary joint to the four-way air 

 valve. The sliding-sleeve assembly of the four- 

 way valve can be shifted endwise along the valve 

 shaft by operating the control lever. 



When the shifter arm on the control lever 

 slides the valve assembly away from the engine, 

 air is directed to the forward clutch. The four- 

 way valve makes the connection between the air 

 supply and the forward clutch, as follows: there 

 are eight neutral ports which connect the cen- 

 tral air supply passage in the valve shaft with 

 the sealed air chamber in the sliding member. 

 In the neutral position of the four-way valve, as 

 shown in figure 22-39, the air chamber is a 

 dead end for the supply air. In the forward 

 position of the valve, the sliding member un- 

 covers eight forward ports, which connect with 

 the forward passages conducting the air to the 

 forward clutch. The air now flows through the 

 neutral ports, air chamber, forward ports, and 

 forward passages to inflate the forward clutch 

 gland. As long as the valve is in the forward 

 position, the forward clutch will remain inflated 

 and the entire forward air system will remain 

 at a pressure of 100 psi. 



LUBRICATION.— On most large gear units, 

 a separate lubrication system is used. One 

 lubrication system is shown in figure 22-40. 

 Oil is picked up from the gear box by an electric- 

 driven gear-type lubricating oil pump and is 

 sent through a strainer and cooler. After being 

 cleaned and cooled, the oil is returned to the 

 gear box to cool and lubricate the gears. In 

 twin installations, such as shown in figure 22- 

 40 a separate pump is used for each unit and a 

 standby pump is interconnected for emergency 

 use. 



Hydraulic Clutches or Couplings 



The fluid clutch (coupling) is widely used 

 on Navy ships. The use of hydraulic coupling 



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