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A cross shaft with a +908 crank pin offsetbalances the first order masses. A thick intermediate web isessential for reasons of strength.High engine powers not only require large displacementbut also large numbers of cylinders. V10 engines haveattained importance between V8 and V12 engines. Largerdiesel engines are usually based on cost cutting modularengine concepts. The balancing of V8 engine masses nor-mally dictates a uniform V angle of 908. First order freemoments of inertia no longer occur in ‘‘normal balancing’’(see Sect. 8.3.3). Appropriate throw configuration (firingsequence) can additionally minimize second order freemoments of inertia.A908 V series can be designed more broadly for four-stroke medium speed engines and not only include V8, V10and V12 but also V16 and V20 variants (e.g. MTU 2000(CR), DEUTZ-MWM 604 [8-27], 616 and 620, MTU 396and 4000). Figure 8-8 presents an MTU 4000 series V16engine. The best standard V angle for other numbers andincrements of cylinders has to be determined allowing forthe particular boundary conditions. While the free massactions are increasingly less significant as of 12 cylindersand upward, non-uniform ignition intervals on the otherhand require effective vibration damping. A V angle of 908still creates sufficient space to house auxiliary units betweencylinder banks. However, increasing numbers of cylindersreduce the V angle produced purely mathematically. Anengine grows increasingly top heavy whenever auxiliaryunits continue to be mounted. This aspect may also influ-ence the decision to select a proportionately larger V anglefor V12 and V16 engines as in the MTU 595 series [8-28](728 instead of 608 or 458).Fig. 8-8 MTU 4000 series V16 diesel engine (source: MTU FriedrichshafenGmbH)Fig. 8-7 VW I5 TDI1 diesel engine crankshaft (with vibration damperintegrated in the engine front side counterweight [8-22]) 8.2 Crankshaft
Assembly Loading8.2.1 Preliminary Remarks on Component Loadingin the Crankshaft AssemblyPistons, piston pins, the connecting rod and the crankshaft(crankshaft assembly) as well as the flywheel all form a reci-procating piston engine’s crankshaft assembly. The compo-nents of the crankshaft assembly are not only subject to highgas forces but also tremendous acceleration (mass actions).Conflicting demands such asminimummass on the one handand high stiffness and endurance strength on the other pre-sent a challenge to component design. Since this handbookhandles the components of the piston and connecting rodelsewhere (see Sect. 8.6), these remarks about their loading arekept brief.8.2.2 Remarks on Piston and ConnectingRod LoadingPiston mass contributes substantially to the oscillating massand is thus subject to strict criteria of lightweight construc-tion. Combustion chamber pressure and temperature highlystress a piston thermomechanically. Highly thermally con-ductive, aluminum piston alloys combine low materialdensity with high thermal load relief. However, their use indiesel engines reaches its physical limits at firing pressuresabove 200 bar.The piston force (Eq. (8-1)) is supported in the piston pinboss. The inertial force counteracts the gas force, decreasingthe load as speed increases. The piston skirt acts on thecylinder bore surfaces with the kinematically induced sidethrust (Eq. (8-3)). Gas force predominantly stresses dieselengine pistons. In high speed gasoline engines, the stress ofinertial force may outweigh the stress of the gas force. Pre-venting the piston pin boss from overstressing necessitateslimiting the contact pressure and minimizing pin deforma-tion (bending deflection and oval deformation). Diesel enginepiston pins have to be engineered particularly solidly eventhough they contribute to the oscillating mass.The connecting element between the piston pin and crankpin, the connecting rod is pided into an oscillating and arotating mass component (Eqs. (8-24) and (8-25)). Light-weight aluminum connecting rods only play a role in verysmall engines. Titanium alloys are out of the question forreasons of cost and primarily remain reserved for racing. Justas for pistons, the reduction of mass and the optimization ofstructural strength are inseparably interconnected.The gas force (ITDC) and oscillating inertial force (ITDCand GETDC) load a diesel engine’s connecting rod shankwith pulsating compressive stress. Above all, it must be ade-quately protected against buckling. Alternating bending stressof a connecting rod shank caused by transversal accelerationis less important at diesel engines’ level of speed. Inertial forcegenerates pulsating tensile and bending stress in the connect-ing rod small end and the eye. Bending, normal and radialstresses act in the curved eye cross section.