tankinbeans wrote:I still can't quite wrap my mind around how a 3 cylinder engine works. I always thought there had to be at least one cylinder in each stage of the combustion cycle (intake, compression, combustion, exhaust) at all times, and with fewer than 4 cylinders that's not possible. For that matter the I5 in my friend's car confounds me no end.
"A five-cylinder engine gets a power stroke every 144 degrees (720° ÷ 5 = 144°). Since each power stroke lasts 180 degrees, this means that a power stroke is always in effect. Because of uneven levels of torque during the expansion strokes divided among the five cylinders, there are increased secondary-order vibrations. At higher engine speeds, there is an uneven third-order vibration from the crankshaft which occurs every 144 degrees. Because the power strokes have some overlap, a five-cylinder engine may run more smoothly than a non-overlapping four-cylinder engine, but only at limited mid-range speeds where second and third-order vibrations are lower."
"Straight-three engines employ a crank angle of either 120° or 180°.
120° cranks are 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 engine. The use of a balance shaft in an antiphase to that vibration produces a smoothly running engine.
A 180° crankshaft can be found in straight-three engines made by motorcycle manufacturer Laverda and in small cars such as the Suzuki Cultus 1.0. In these engines, the outer pistons rise and fall together like a 360° straight-two engine. The inner cylinder is offset 180° from the outer cylinders. In these engines, cylinder number one fires, then 180° later cylinder number two fires, and then 180° later cylinder number three fires. There is no power stroke on the final 180° of rotation."