8.1 Designs and Mechanical Propertiesof Crankshaft Assemblies8.1.1 Function and Requirements of CrankshaftAssembliesTogether with both the piston pins and the crankshaft’scrank pins, the connecting rod in reciprocating pistonengines converts oscillating piston motion into rotarycrankshaft motion. Running smoothness is a universallyimportant criterion for the design of crankshaft assemblies.High speed has priority in gasoline engines, thus making aminimum of moving masses an absolute imperative. Theemphasis shifts somewhat for diesel engines. Firing pres-sures can be twice as high as in gasoline engines and con-tinue to increase as the size increases. Thus, controlling theeffects of the gas force is the primary challenge.In conjunction with direct injection and one or two-stageexhaust gas turbocharging and intercooling, car dieselengines now attain the volumetric power outputs of gasolineengines. Moreover, cuts in fuel consumption (reduction ofCO2 emission), strict emission laws and lightweight andincreasingly compact designs that do not sacrifice reliabilityare currently driving engine development. However, in prin-ciple, steadily increasing ignition and injection pressuresresult in ‘‘harsher’’ combustion. This inevitably creates moreproblems with acoustics and vibrations as demands for com-fort increase. Now common in diesel cars,multiple injections,optimized vibration damping, camshaft drives shifted to theflywheel-side, dual-mass flywheels and partial encapsulationsserve to improve modern diesel engines’ acoustic and vibra-tion performance. 35693
Not least, the steadily increasing ampli-tudes of the gas torque characteristic make using the enginemounting and the entire power train to control crankshaftassembly vibrations, improve mass balancing and reduce theexcitation of vibrations even more important. In Europe, thediesel engine has evolved from merely being the primary  commercial vehicle engine to also being a frequently usedcar engine.A modern diesel engine’s tremendous mechanical stress onthe crankshaft assembly also has to be accommodated. Crank-shaft assembly components require a structural design opti-mized for structural strength, stiffness and mass. Knowledgeof locally present fatigue limits of materials that affect compo-nents has not quite kept pace with the simulation of loadingconditions, which has become quite precise in the meantime.This reveals a potential weak point in fatigue strength simula-tions in the limit range. Thus, evenmore precisemeasurementof the practical impact of technological influences and qualityfluctuations in manufacturing will be essential in the future.8.1.2 Crankshaft Assembly ForcesThe literature includes numerous studies devoted to the crank-shaft assembly of a reciprocating piston engine (c.f. [8-1, 8-2]).Varying with the crank angle j, the piston force FK(j)actson the crankshaft assembly on the piston side. According toFig. 8-1, this ensues fromthe superimposition of the oscillatinginertial force Fmosz(j)onthegasforce FGas(j):FK ¼ FGas þ Fmosz (8-1ÞThe gas force FGas(j) is the product of the cylinder pressurepZ(j) and the area of the piston AK. The cylinder pressurecharacteristic can be measured by cylinder pressure indicationor calculated with the aid of engine process simulation.The oscillating inertial force can be measured according toEq. (8-30). When c is the pivoting angle of the connectingrod, the connecting rod force FPlin a housing-related refer-ence system follows from the piston force FK:FPl ¼ FKcos c(8-2ÞThe connecting rod’s oblique position causes the piston sidethrust FKN: to act on the area of the cylinder bore surface:FKN ¼ FK tan c [1]