Straight-3
From Wikipedia, the free encyclopedia
A straight-3 or inline-3 is an internal combustion engine with three cylinders arranged in a straight line side by side.
Most straight-3 engines employ a crank angle of 120° and are thus rotationally balanced; however, since the three cylinders are offset from each other, the firing of the end cylinders induces a rocking motion from end to end, since there is no opposing cylinder moving in the opposite direction as in a rotationally balanced straight six. The use of a balance shaft in antiphase to that vibration produces a smoothly running engine.
An exception to the 120° crankshaft can be found in some of the straight-3 engines made by motorcycle manufacturer Laverda. In these engines, sometimes referred to as 180° triples, the outer pistons rise and fall together like a 360° straight-2. The inner cylinder is offset 180° from the outer cylinders. In these engines cylinder 1 fires, 180° later cylinder 2 fires, and then 180° later cylinder 3 fires. There's no power stroke on the final 180° of rotation--much like a 4-cylinder engine that's missing the fourth cylinder.
[edit] Automobile use
The straight-3 is the smallest engine in use in modern cars, generally for engine displacements of around 1.0L. Cars in the 'super-mini' class often use them on base models, as do the Japanese Keicars. A straight-3 is also used in the Suzuki Swift, its American cousins: the Geo Metro and the Chevrolet Sprint, the Subaru Justy, the Honda Insight, and also two stroke Saabs (93 - 96). One experimental Saab had two transverse straight-3 engines, the Saab Monster. Recently the straight-3 has appeared in the Smart Fortwo.
The smallest straight-3 engine was the 543 cc Suzuki F5A used in the 1982 Cervo. Smart currently produces a diminutive 799 cc diesel straight-3, the smallest ever. Most straight-3 engines fall below 1.2 liters, with a 1,198 cc Volkswagen unit seen as the largest petrol unit. A 1.8 L (1779 cc) diesel was produced by VM Motori to 1984 Alfa Romeo 33 1.8 TD, the largest straight-3 produced for automotive use.
[edit] Motorcycle use
4-stroke :
Aprilia, Laverda, Triumph, Yamaha, BMW.
The Triumph Rocket III has a 2,294 cc straight-3 engine, currently the largest engine in a motorcycle being made by a major manufacturer.
2-stroke :
[edit] References
http://www.laverdamania.com/millegb.htm
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