Engine balance

Engine balance refers to how the inertial forces produced by moving parts in an internal combustion engine or steam engine are neutralised with counterweights and balance shafts, to prevent unpleasant and potentially damaging vibration. The strongest inertial forces occur at crankshaft speed (first-order forces) and balance is mandatory, while forces at twice crankshaft speed (second-order forces) can become significant in some cases.

Engine balance refers to how the inertial forces produced by moving parts in an internal combustion engine or steam engine are neutralised with counterweights and balance shafts, to prevent unpleasant and potentially damaging vibration. The strongest inertial forces occur at crankshaft speed (first-order forces) and balance is mandatory, while forces at twice crankshaft speed (second-order forces) can become significant in some cases. === Flat engines=== flat-twin engine viewed from above, showing the offset between the left & right cylinders]] A 'flat' engine is not necessarily a 'boxer' engine. A 'flat' engine may either be a 180-degree V engine or a 'boxer' engine. A 180-degree V engine as used in the Ferrari 512BB has opposed cylinder pairs whose connecting rods use the same crank throw. Contrary to this, in a 'boxer' engine, as applied in BMW motorcycles, each connecting rod has its own crank throw which is positioned 180 degrees from the crank throw of the opposed cylinder. Flat-twin engines typically use 180° crankshafts and separate crank throws and have the following characteristics: Primary and secondary reciprocating plane balance is perfect. Primary and secondary rotating plane imbalance is present. Flat-four engines typically use a left–right–right–left crankshaft configuration and have the following characteristics: Primary imbalances are caused by the rocking couples of the opposing pistons being staggered (offset front to back). The intensity of this rocking couple is less than a straight-four engine, since the pairs of connecting rods swinging up and down move at different centre of gravity heights. Secondary imbalances are minimal. Flat six engines typically use a boxer configuration and have the following characteristics: An evenly spaced firing interval with overlapping power strokes. A simple three-into-one exhaust for each cylinder bank provides uniform scavenging, since the engine is effectively behaving like two separate straight-three engines in this regard. Primary reciprocating plane and rotating plane imbalances are present due to the distance along the crankshaft between opposing cylinders. A flat-six engine would have perfect primary balance if fork-and-blade connecting rods were used. Secondary imbalances are minimal, because there are no pairs of cylinders moving in phase, and the imbalance is mostly cancelled out by the opposing cylinder. Torsional imbalances are lower than straight-six engines, due to the shorter length of a flat-six engine. ==See also== Balancing machine Noise, vibration, and harshness ==References== Citations Sources it:Contralbero nl:Balansas pt:Equilíbrio de motores de combustão interna

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