曲轴组件的设计英文文献和中文翻译(6)

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inner’’ dimensions are the main pin width and crank pinwidth, the related journal diameters and the crankshaft webthickness and width (Fig. 8-9). The flywheel flange is locatedon the output end with its bolt hole circle and centering. Theshaft’s free end is constructed as a shaft journal for theattachment of the belt pulley, vibration damper and soforth. Powered by the crankshaft, the camshaft drive may bemounted on the front end or, frequently in diesel engines, onthe flywheel end for reasons of vibrations.The number of throws depends on the number of cylindersz and the number of main crankshaft bearings ensuing fromthe design (I engine: z throws, z + 1 main pins, V engine: z/2double throws, z/2 +1 main pins).The distance between cylinder bore center lines aZ – thecylinder bore diameter DZ and the width of the wall betweencylinders DaZ – defines the crank spacing in inline engines.Conversely, unlike corresponding inline engines, ‘‘inner’’dimensions may be relevant for cylinder clearance in Vengines when, for instance, enlarged bearing width, rein-forced crankshaft webs and a double throw with crank pinoffset and intermediate web become necessary. ‘‘Inner’’dimensions determine the crank spacing anyway when thereare z +1 main bearings, i.e. a double throw is dispensed with,particularly in the so-called ‘‘Boxer’’ design with (horizontally) opposing cylinder pairs with crankshaft throwsoffset by 1808.8.2.3.2
Crankshaft Materials and ManufacturingForged crankshafts made of high grade heat-treated steels arebest able to meet the high requirements off dynamic strengthand, in particular, stiffness too. Less expensive microalloyedsteels heat-treated by controlled cooling fromthe forging heat(designated ‘‘BY’’) are increasingly being used. In less loadedcar engines (primarily naturally aspirated gasoline engines),they may also be cast from nodular graphite cast iron (nod-ular cast iron of the highest grades GJS-700-2 and GJS-800-2)[8-29, 8-30]. This reduces the costs of both manufacturingand machining a blank. 8 to 10% less material density thansteel and the option of a hollow design additionally benefitcrankshaft mass. A significantly lower Young’s modulus,lower dynamic strength values and less elongation at fracturethan steel have to be accepted (the label ‘‘–2’’ stands for aguaranteed 2%).Cost effective machining limits the materials’ tensilestrength to approximately 1,000 MPa. Hence, measures thatenhance the fatigue strength of the transition and the concavefillet radii, which are critical to loading, between the journaland web are indispensible. Mechanical, thermal andthermochemical processes are employed. Pressure forming,roller burnishing [8-31] and shot peening, inductive and casehardening and nitriding build up intrinsic compressive stres-ses and strengthen the surface areas of materials (Fig. 8-10).Each process enhances fatigue strength with varyingquality. Nitriding’s penetration is comparatively slight, thusmaking it impossible to entirely rule out fatigue failures in thecore structure near the surface. The journals in vehicleengines are also hardened. Inductive hardening is quite alow cost process [8-32, 8-33]. The expense connected withcase hardening on the other hand limits its cost effectiveapplication to larger crankshafts. The sequence of concavefillets must be followed when they are hardened because ofdistortion. The high heat output required during a very briefheating-up period, makes thin intermediate webs or oil boresin a shallow depth beneath the concave fillets critical duringtempering.Casting and forging necessitate designing blanks adaptedto the manufacturing process. Sand (green sand or bondedsand cores), shell mold, evaporative pattern or full moldcasting are used for cast crankshafts. Large lots are dropforged (the fiber flow facilitating fatigue strength). Largecrankshafts on the other hand are hammer forged (poorerfiber flow). Fiber flow forging is employed for larger crank-shafts and smaller quantities. The shaft is cranked