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Straight-eight engine
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Straight-eight engine
The straight-eight engine (also known as a inline-eight engine; abbreviated as I8) is an eight-cylinder internal combustion engine with all eight cylinders mounted in a straight line along the crankcase. The type has been produced in side-valve, IOE, overhead-valve, sleeve-valve, and overhead-cam configurations.
A straight-eight can be timed for inherent primary and secondary balance, with no unbalanced primary or secondary forces or moments. However, crankshaft torsional vibration, present to some degree in all engines, is sufficient to require the use of a harmonic damper at the accessory end of the crankshaft. Without such damping, fatigue cracking near the rear main bearing journal may occur, leading to engine failure.
Although an inline six-cylinder engine can also be timed for inherent primary and secondary balance, a straight-eight develops more power strokes per revolution and, as a result, will run more smoothly under load than an inline six. Also, due to the even number of power strokes per revolution, a straight-eight does not produce unpleasant odd-order harmonic vibration in the vehicle's driveline at low engine speeds.
The smooth running characteristics of the straight-eight made it popular in luxury and racing cars of the past. However, the engine's length demanded the use of a long engine compartment, making the basic design unacceptable in modern vehicles. Also, due to the length of the engine, torsional vibration in both crankshaft and camshaft can adversely affect reliability and performance at high speeds. In particular, a phenomenon referred to as "crankshaft whip," caused by the effects of centrifugal force on the crank throws at high engine rpm, can cause physical contact between the connecting rods and crankcase walls, leading to the engine's destruction. As a result, the design has been displaced almost completely by the shorter V8 engine configuration.
The first straight-eight was conceived by Charron, Girardot et Voigt (CGV) in 1903, but never built.[page needed] Great strides were made during World War I, as Mercedes made straight-eight aircraft engines like the Mercedes D.IV. Advantages of the straight-eight engine for aircraft applications included the aerodynamic efficiency of the long, narrow configuration, and the inherent balance of the engine making counterweights on the crankshaft unnecessary. The disadvantages of crank and camshaft twisting were not considered at this time, since aircraft engines of the time ran at low speeds to keep propeller tip speed below the speed of sound.
Unlike the V8 engine configuration, examples of which were used in De Dion-Bouton, Scripps-Booth, and Cadillac automobiles by 1914, no straight-eight engines were used in production cars before 1920.
Italy's Isotta Fraschini introduced the first production automobile straight-eight in their Tipo 8 at the Paris Salon in 1919 Leyland Motors introduced their OHC straight-eight powered Leyland Eight luxury car at the International Motor Exhibition at Olympia, London in 1920. The Duesenberg brothers introduced their first production straight-eight in 1921.
Straight-eight engines were used in expensive luxury and performance vehicles until after World War II. Bugattis and Duesenbergs commonly used double overhead cam straight-eight engines. Other notable straight-eight-powered automobiles were built by Daimler, Mercedes-Benz, Isotta Fraschini, Alfa Romeo, Stutz, Stearns-Knight and Packard. One marketing feature of these engines was their impressive length — some of the Duesenberg engines were over 4 ft (1.2 m) long, resulting in the long hoods (bonnets) found on these automobiles.
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Straight-eight engine
The straight-eight engine (also known as a inline-eight engine; abbreviated as I8) is an eight-cylinder internal combustion engine with all eight cylinders mounted in a straight line along the crankcase. The type has been produced in side-valve, IOE, overhead-valve, sleeve-valve, and overhead-cam configurations.
A straight-eight can be timed for inherent primary and secondary balance, with no unbalanced primary or secondary forces or moments. However, crankshaft torsional vibration, present to some degree in all engines, is sufficient to require the use of a harmonic damper at the accessory end of the crankshaft. Without such damping, fatigue cracking near the rear main bearing journal may occur, leading to engine failure.
Although an inline six-cylinder engine can also be timed for inherent primary and secondary balance, a straight-eight develops more power strokes per revolution and, as a result, will run more smoothly under load than an inline six. Also, due to the even number of power strokes per revolution, a straight-eight does not produce unpleasant odd-order harmonic vibration in the vehicle's driveline at low engine speeds.
The smooth running characteristics of the straight-eight made it popular in luxury and racing cars of the past. However, the engine's length demanded the use of a long engine compartment, making the basic design unacceptable in modern vehicles. Also, due to the length of the engine, torsional vibration in both crankshaft and camshaft can adversely affect reliability and performance at high speeds. In particular, a phenomenon referred to as "crankshaft whip," caused by the effects of centrifugal force on the crank throws at high engine rpm, can cause physical contact between the connecting rods and crankcase walls, leading to the engine's destruction. As a result, the design has been displaced almost completely by the shorter V8 engine configuration.
The first straight-eight was conceived by Charron, Girardot et Voigt (CGV) in 1903, but never built.[page needed] Great strides were made during World War I, as Mercedes made straight-eight aircraft engines like the Mercedes D.IV. Advantages of the straight-eight engine for aircraft applications included the aerodynamic efficiency of the long, narrow configuration, and the inherent balance of the engine making counterweights on the crankshaft unnecessary. The disadvantages of crank and camshaft twisting were not considered at this time, since aircraft engines of the time ran at low speeds to keep propeller tip speed below the speed of sound.
Unlike the V8 engine configuration, examples of which were used in De Dion-Bouton, Scripps-Booth, and Cadillac automobiles by 1914, no straight-eight engines were used in production cars before 1920.
Italy's Isotta Fraschini introduced the first production automobile straight-eight in their Tipo 8 at the Paris Salon in 1919 Leyland Motors introduced their OHC straight-eight powered Leyland Eight luxury car at the International Motor Exhibition at Olympia, London in 1920. The Duesenberg brothers introduced their first production straight-eight in 1921.
Straight-eight engines were used in expensive luxury and performance vehicles until after World War II. Bugattis and Duesenbergs commonly used double overhead cam straight-eight engines. Other notable straight-eight-powered automobiles were built by Daimler, Mercedes-Benz, Isotta Fraschini, Alfa Romeo, Stutz, Stearns-Knight and Packard. One marketing feature of these engines was their impressive length — some of the Duesenberg engines were over 4 ft (1.2 m) long, resulting in the long hoods (bonnets) found on these automobiles.
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