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Nonethe-less, a balance shaft (counter-) rotating at crankshaft speed isnow used in Smart/Mitsubishi I3 diesel engines [8-18].The majority of car diesel engines are inline four-cylinderengines. The I4 engine does not have any first order freeinertial forces or any first and higher order free moments ofinertia. However, the inertial forces of all four cylinders addup in the second order.What is more, ignition frequency andthe second order coincide poorly.Without proper reinforcingmeasures, an engine-transmission unit’s lowest naturalbending frequency may be too close to the correspondingexcitation. Unpleasant humming noises in the passengercompartment are the consequence. In light of the increaseddemands on comfort, two balance shafts counterrotating atdouble speed are increasingly being employed to improverunning smoothness (see [8-19]).Reservations about the I5 engine are in turn based on theconflicting goals when balancing masses. It is designed at theexpense of an unfavorably large first or second order tiltingmoment (see Sect. 8.3.4) [8-20, 8-21]. The former cannot befully balanced by counterweights in the crankshaft alone. Alarge crankshaft is comparatively heavy and, since it oscillates,the latter requires a pair of balance shafts rotating in oppositedirections at double speed. Despite the recent development ofnew R5 diesel engines (Fig. 8-7 [8-22]), this design appears tobe losing significance again.I4 diesel engines’ high torque and increased volumetricpower output make it possible to utilize them as basic motorsfor cars above medium size. Moreover, a trend toward V6diesel engines is discernible. Vehicle package, crash length andthe option of transverse engine installation (an increasingpersity of variants) are generally influencing this develop-ment in all cars. While the I6 engine is built longer, its out-standing running smoothness (no free mass actions even ofthe fourth order) is impressive. It enjoys an outstanding reputation in commercial vehicles too, especially from theperspective of cost and benefit.V6 engines’ first and second order free moments of inertiaprevent them from attaining this quality of running smooth-ness (the special case of aV = 1808 not being considered here).However, a compromise, so-called normal balancing (seeSect. 8.3.3) makes it possible to completely balance the firstorder free moments of inertia for V angles of 608 – the crankpin offset likewise being +608 – and 908. However, 908 is wellknown to translate into unequal ignition intervals at thethrow angle of 1208 typical for V6 engines. Thus, based onEq. (8-13) already mentioned in Sect. 8.1.3.4, equalization inthe AUDI V6TDI1 engine [8-23] requires a crank pin offsetof +308. It is +488 in DaimlerChrysler’s V6 diesel engine withan atypical V angle of 728 [8-24]. This produces a negatively(counter-) rotating first order moment of inertia. A balanceshaft likewise rotating negatively at crankshaft speed providescomplete balancing.The V8 design with a 908 V angle is widespread in largerdiesel engines. Neither first and second order free inertialforces nor second order free moments of inertia occur inthis configuration. ‘‘Normal balancing’’ (see Sect. 8.3.3) canin turn fully balance the remaining first order freemoments of inertia. The non-uniform ignition intervalsper cylinder bank (without continuous alternate ignitionof both cylinder banks) are acoustically perceptibletogether with the gas exchange. This can only be preventedwith a ‘‘flat’’ crankshaft, i.e. a crankshaft offset by 1808instead of 908 (I4 crankshaft), while accepting secondorder free mass actions.A V8 engine only deviates from the V angle of 908 for validreasons, e.g. 758 in DaimlerChrysler’s OM629 V8 car dieselengine [8-25]. A uniform ignition interval is in turn givenprecedence with a crank pin offset of +158. Hence, theaforementioned first order balance shaft is used. It is housedin the main oil gallery to save space. SKL’s 8VDS24/24ALdiesel engine with a V angle of 458 was designed for narrowerengine width [8-26].
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