CHAPTER 3POWER TRAIN AND PROPULSION SYSTEMSAs a GS supervisor, you will primarily supervise theoperation and maintenance of the power train equipmentand controllable pitch propeller systems. This chapterwill focus on the maintenance and repair of the mainpropulsion systems needed to support the operations ofthe main propulsion gas turbine engines.After studying the information in this chapter, youshould have a well-rounded understanding of the drivetrain equipment and propulsion plant systems in gasturbine-powered ships. You should better understandt e r m s o f n o r m a l o p e r a t i o n s , s o m e c o m m o nmalfunctions, and your role as the GS supervisor.POWER TRAINIn Gas Turbine Systems Technician (Electrical)3/Gas Turbine Systems Technician (Mechanical) 3,volume 1, NAVEDTRA 10563, there is a fairly detaileddescription of the various power train arrangementsused by gas turbine-powered ships. You may wish toreview those chapters on such items as construction,principles of operation, nomenclature, and operatingparameters. In this section, we will cover some of thepower train system tests, inspections, adjustments, andrepairs that you will be responsible for as a supervisor.MAIN REDUCTION GEARThe inspection procedures and problems that occurin main reduction gears (MRGs) are basically the samefor any system. It will not be necessary to differentiatebetween classes of ships in this section, except wherespecific differences exist. Additional information on theinspection and adjustment of gear trains can be found inNaval Ships’ Technical Manual (NSTM), chapter 9420,“Propulsion Reduction Gears, Couplings, andAssociated Components,” NAVSEA 0901-LP-420-0002, or in the manufacturer’s technical manual for yourspecific installation.Inspection and RepairBefore reading descriptions and details on MRGinspections, you need to be familiar with theterminology used throughout this section. The majorityof the following gear nomenclature also applies tohelical gears. Figure 3-1 may be of help on some ofthese definitions.RATIO. The number of gear teeth divided by thenumber of teeth in the pinion.LINE OF ACTION. The locus of the points ofcontact as the profiles go through mesh. This linepasses through the pitch point and is tangent to thebase circle.HELIX ANGLE (fig. 3-l). The angle formed by atooth and a plane passing through the axis of thegear.PRESSURE ANGLE (fig. 3-1). The angle betweenthe line of action and the line tangent to the pitchcircles.TRANSVERSE DIAMETRAL PITCH. The ratioof the number of teeth to the number of inches ofthe pitch diameter.NORMAL DIAMETRAL PITCH. The transversediametral pitch divided by the cosine of the helixangle.CHORDAL TOOTH THICKNESS (normal) (fig.3-1). The thickness of the tooth measured on thechord of the pitch diameter in the normal plane.CIRCULAR PITCH (axial) (fig. 3-l). The lengthof the arc on the pitch circle between similar pointsof adjacent teeth in the plane of rotation.CIRCULAR PITCH (normal) (fig. 3-l). The lengthof the arc on the pitch circle between similar pointsof adjacent teeth in the normal plane.OUTSIDE DIAMETER (fig. 3-l). The diametermeasured over the tops of the teeth.PITCH DIAMETER (fig. 3-l). The diameter of thepitch circle.BASE DIAMETER (fig. 3-l). The circle fromwhich a line is unwound to generate the involutecurve.ROOT DIAMETER (fig. 3-1). The diameter of theroot circle.ADDENDUM (fig. 3-1). The distance from thepitch circle to the top of the tooth.3-1
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