Principles of naval engineering - Historic Naval Ships Association

Chapter 22. -DIESEL AND GASOLINE ENGINESIDLER GEARFORWARD ROTATION75.252Figure 22-36. — Forward and reverse gear trainsfor Gray Marine engines.The clutch operating lever moves the throwoutfork, which in turn shifts the sliding sleevelengthwise along the forward shaft. When theoperating lever is placed forward, the slidingsleeve is forced backward. In this position thelinkages of the spring-loaded mechanism pullthe floating pressure plate against the forwarddisk, and cause forward rotation. When the operatinglever is pulled back as far as it can go,the sliding sleeve is pushed forward. In thisposition, the floating pressure plate engages thereverse disk and back plate for reverse rotation.The clutch has a positive neutral which isset by placing the operating lever in a middleposition. Then the sliding sleeve is also in amiddle position, and the floating plate rotatesfreely between the two clutch disks. (The onlycontrol that the operator has is to cause thefloating plate to bear heavily against either theforward disk or the reverse disk, or to put thefloating plate in the positive neutral positionso that it rotates freely between the twodisks.)The reversing gear unit is lubricated separatelyfrom the engine by its own splash system.The oil level of the gear housing should neverbe kept over the high mark because too muchoil will cause overheating of the gear unit. Theoil is cooled by air which is blown through thebaffled top cover by the rotating clutch. Greasefittings are installed for bearings not lubricatedby the oil.JOE'S DOUBLE CLUTCH REVERSE GEAR.-A gear mechanism found on many power boatsis Joe's double clutch reverse gear. The installationof a typical Joe's reverse gear andclutch assembly for the Navy type DC engineis shown in figure 22-37. The drive from theengine crankshaft is taken into the clutch andreverse gear housing by an extension of thecrankshaft drive gear. The crankshaft rotationis transmitted to the reduction gear shaft throughthe clutch and the reverse gear unit.If one could open the clutch and reverse gearhousing and watch the reverse gear drum andthe reduction gear shaft while the engine is running,the following operation would be observed:When the operating lever is thrown forward,the drum and reduction gear shaft rotate in thesame direction as the engine crankshaft. Thiscauses forward rotation of the propeller.In the intermediate position of the operatinglever, the drum rotates but the reduction gearshaft remains stationary. This is the neutralsetting.Forward rotation is obtained by dual clutchaction while reverse rotation is obtained throughthe operation of the planetary gears. The unitconsists of a housing enclosing a split conicalclutch and a multi-plate friction clutch andgearing. Additional components include the collarand yoke and an outer brake band with anoperating toggle mechanism. Movement of thesliding collar selects the direction of rotation.When the operating lever is placed in theforward position, the linkage between the leverand the collar and yoke assembly slides thecollar lengthwise to the left along the reductiongear shaft. This motion operates the toggleassembly which, in turn, drives the threeplungers to the right, pressing them hard againstthe disk clutch.When the plungers are driven hard againstthe disk clutch, the disks are locked togetherby friction. This locks the drum housing to the585