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The crossplane or cross-plane is a crankshaft design for piston engines with a 90° angle (phase in crank rotation) between the crank throws.〔See Crankshaft for "crank throw".〕 The crossplane crankshaft is the most popular configuration used in V8 road cars. Crossplane crankshaft could be used in many cylinder configurations to have an evenly spaced firing as long as the number of cylinders is multiples of four in two-stroke engines, or multiples of eight in 4 stroke engines. Unless the crank pins have big-end phase-offset, the V-angle requirement must be met for an evenly spaced firing on V configurations as listed below. 2 cycle: L4, L8, L12, L16, V4 (V-angle of 90°), V8 (45°,90° or 135°), V12 (30°,60°,90°,120° or 150°), V16 (22.5°,45°,67.5°,90°,112.5°,135° or 157.5°), flat4, flat8, flat12, flat16, etc. 4 cycle: L8, L16, V8 (V-angle of 90°), V16 (45°,90° or 135°), flat8, flat16, etc. However, crossplane crankshaft has been used on other 4 stroke configurations like L2, L4, V2 and V4 engines with unevenly spaced firing when its prominent advantage of smaller secondary (non-sinusoidal) vibration, which increases exponentially with crankshaft rotational speed, out-weigh the disadvantages like the imbalance in firing spacing and the increase in rocking vibration. ==90° V8 crankshaft== The most common crossplane crankshaft for a 90° V8 engine has four crankpins, each serving two cylinders on opposing banks, offset at 90° from the adjacent crankpins. The first and last of the four crank pins are at 180° with respect to each other as are the second and third, with each pair at 90° to the other, so that viewed from the end the crankshaft forms a cross. The crankpins are therefore in two planes ''crossed'' at 90°, hence the name ''crossplane''. A crossplane V8 crankshaft may have up to nine main bearings in the case of an eight throw design, and usually has five bearings supporting four throws each with a shared crank pin. Crossplane V8 engines have unevenly spaced firing patterns within each cylinder bank, often producing a ''distinctive burble'' in the exhaust note, but an even firing pattern overall. Their non-sinusoidal imbalance, owing to the lack of pistons that move together in the reciprocal phase, is half as strong and double as frequent as in the flatplane design that does have piston pairs moving together. In the absence of balancer shafts, the disadvantages include rotating plane imbalances on 1.rotating mass (crankshaft), 2.reciprocating mass (pistons and conrods), 3.torque generation and 4.compression, all of which generate rocking vibrations.〔See Engine balance.〕 These imbalances can be countered to varying degrees with heavy counterweights on each crank throw, so most crossplane V8s have very heavy crankshafts. Early Chrysler Hemi V8 had heavy counterweights, but the middle two positions on both sides of the center main bearing (the third of 5 mains) did not have any counterweight, as these positions are located close to the center of engine and deemed ineffective to counter rocking motions. Another disadvantage is the aforementioned unevenly spaced firing within a bank of four cylinders, which can be mitigated by what is called a Bundle of Snakes as described below. The other prominent design for a V8 crankshaft is the ''flatplane'' crankshaft, with all crankpins in the same plane and the only offset being 180°. Early V8 engines, modern racing engines and some others have the flatplane crankshaft, which is similar to that used in a straight four or flat-four engine. They lack the V8 burble but have double as strong (and half as frequent) secondary vibration of the crossplane design, and do not require the large crankshaft counterweights. Inherent balance of the reciprocating mass is like a pair of straight fours, and modern designs often incorporate a balance shaft for smoothness. When built without balancer shafts that add to the overall rotating mass, flatplane designs have the least flywheel effect of any V8s, which allows them to be quicker to rev up and down. The crossplane design was first proposed in 1915, and developed by Cadillac and Peerless, both of whom produced flatplane V8s before introducing the crossplane design. Cadillac introduced the first crossplane in 1923, with Peerless following in 1924. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「crossplane」の詳細全文を読む スポンサード リンク
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