Where can I find information on the net for torsional and balance for inline
3 cylinder engines ?I saw two sites but I dont remember where. The two proposed the same solution (a balance shaft running at crank speed), but for differents reason. One said because the engine had a rotating move centered on middle cyl. (both cranckshaft end would do opposite circles). The other said because the engine would have a oscillating move up down centered on middle cyl.
Thanks.
F.
Read up on Mazda's rotary engines. There's lots of information on the harmonics and firing orders of piston engines and how they compare to rotaries. Very interesting stuff.
As for the three cylinder engines, with that few cylinders you get horrendous torque flux. (You think a four banger is bad, a three cyl feels like ten times worse.) You can certainly feel each cylinder fire, and I'm not exaggerating. I haven't torn down a three banger but I'm sure some of the more "refined" European versions have counter-rotating balance shafts. These help the engine feel smoother as it turns, but does nothing for the torque flux you feel through the driveline.
I think the North American Ford Festiva three banger has the lowliest form of a four stroke IC engine you can find in a wrecking yard.
I don't recall the Ford Festiva ever having any engine other than a 1.3L
4-cyl. I do remember the Geo Metro having a 1.0L 3-cyl., however. I'm a domestic GM guy myself for the most part, but I can't sneeze at a friend's 1989 Festiva (pizza delivery special) that is still running well to this day with over 336,000 miles on the ORIGINAL UNOPENED engine and second transmission. The only failure so far is a transmission, wheel bearing, horn, and some chafed wires for the A/C clutch that shorted out and had to be repaired. Otherwise, it's had gas, oil, batteries, tires, and brake pads.Roger
You can have *BIG* inline 3.
And it is funny they have 3, 5, 6 and 8, but NO 4 cylinder in that serie.
F.
"Miki Kanazawa" a écrit dans le message news: snipped-for-privacy@posting.google.com...
Miki Kanazawa wrote in rec.autos.tech
People who ride motorcycles are well aware of what very few cylinders feel like. Most of us have ridden bikes with 1 or 2 pistons. Some of us have even ridden 3 cylinder bikes. Yes, vibration is a real issue with engines, and the fewer the cylinders, the worse it gets. And if you want to hear every piston fire, listen to a Harley. It sounds as if it is idling at 10 rpm and then accelerates to about a hundred rpm.
VG wrote in rec.autos.tech
By adding weights that go in the opposite direction of the piston, which is what the balancing shaft does. And the crankshaft will also have similar weights. Not to mention a flywheel the size and weight of a Hummer.
Some twins are suprisingly smooth, particularly small displacement 90 degree V-twins, such as my Suzuki SV650, which has perfect primary balance thanks to the 90 degree V layout. Most other twin cylinder configurations need additional counterbalancers or other vibration mitigation measures, with the exception of BMW boxers. The BMW R65 is supposed to be relatively smooth due to its moderate displacement.
Even Harley has gone to chain driven counterbalancers now on one variant of its latest engine, the Twin Cam 88 'B'.
Mark Olson wrote in rec.autos.tech
This is true, but still a 2 cylinder engine has an inherent inbalance. It takes many cylinders to do away with that imbalance. But the 90 degree V twin design allows for easier placement of balance weights on the crankshaft. BMW's have always been noted for their smoothness. However, they have also been noted for having heavy flywheels. The traditional horizontally opposed twin is a very smooth engine. Much smoother than any other twin in its's class. But that also has a price. The torque from that engine design makes the bike want to lean to one side, especially under acceleration. And the heavy flywheels slowed down acceleration. One man, whose name I don't remember, built quite a business machining flywheels on BMW's. He started with his bike, then did friends, and finally branched out by doing an exchange on them.
Uh huh. Because the twin is so rough running.
Inline 3-cylinder engines have been very common in tractors (both diesel and gasoline) for decades and at least one version was offered in GMC trucks back in the 60s. Torque fluctuations are evident in an engine only if the driveline is improperly designed (not enough flywheel mass) or the engine is loaded to the point of stalling. An inline 3 is "half an inline 6" and (as one poster already mentioned) has a whirl mode vibration that the I6 cancels, but other than that doesn't have any really terrible modes that I'm aware of. One of the most-produced small diesels ever was the Detroit Diesel 3-71. Being a two-stroke, it had as many power strokes per crank rotation as a 4-stroke inline 6, but it still lived (and worked) quite well with the 3-cylinder's inherent whirl mode, so it can't be too bad. No balance shafts, either, although some balancing may have been applied to its roots blower driveline.
I4s are pretty bad vibrationally and flexurally, and usually have to have balance shafts to feel truly smooth.
"Perfect?" I thought a 90-degree twin was good, but a boxer twin was the "perfect" one, to the same degree that an inline 6 is the most optimally naturally-balanced inline. Maybe I'm mis-remembering.
Well, Harley's don't even have even firing intervals! Still the best sounding bike engine short of a Ducati, but no paragon of smoothness even WITH balance shafts, I'm sure.
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