solutions for 2-Stroke vibration
solutions for 2-Stroke vibration
(OP)
The vibrations created primarily from the power pulses on single cylinder 2- stroke engines (or any single cylinder) present a problem in my application at idle and low rpm mainly. Soft engine mounts have been created to combat the vibrations with some success. Although the harmonic dampers that are used on automotive engines are designed to deal with a somewhat different set of problems I was wondering if a similar crankshaft mounted device could be employed on the single cylinder engines in an attempt to calm the power pulses mainly at idle and low engine speeds where the frequency is most damaging for the frame in which the engine is mounted. I envision a inner and outer ring with a silicon damping media like this Fluid Damper http://www.fluidampr.com/IMAGES/CUT_AWAY.jpg
I think the penalty imposed by accelerating the mass would be tolerable if the vibration issue could be significantly improved. Any thoughts?
I think the penalty imposed by accelerating the mass would be tolerable if the vibration issue could be significantly improved. Any thoughts?





RE: solutions for 2-Stroke vibration
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: solutions for 2-Stroke vibration
The only place for some form of a crankshaft mounted device is right in front where the air comes in so a diameter of about 4 inches is the practical limit unless it didnt have a solid face in which case 6" may be possible so maybe a skulpted aluminum flywheel with carbide inserts might work? We could also integrate the ignition trigger magnets and timming marks into the assembley. Wondering though what the inertia effects on engine aceleration would be and how to determine the weight required for initial tests. I do have a dyno as well as a whole slew of data aquisition equiptment
A special engine mount would have to be integrated at the beginning of the build so I was dreaming of a bolt on device that would allow installation on a existing platform with relative ease. Thats important from a marketing standpoint.
RE: solutions for 2-Stroke vibration
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: solutions for 2-Stroke vibration
RE: solutions for 2-Stroke vibration
how about ditching the piston engine for a rotapower?
http://www.freedom-motors.com/
The might be able to scale it down for you.
RE: solutions for 2-Stroke vibration
I once saw a beautiful example of such a thing, but I don't think it's in production anymore. It was the starter for an ME262's Jumo 004 jet engine.
Mike Halloran
Pembroke Pines, FL, USA
RE: solutions for 2-Stroke vibration
RE: solutions for 2-Stroke vibration
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: solutions for 2-Stroke vibration
There are 3 major vibrational modes on a single: Crankshaft & conrod circular vibration, which can be balanced out by crankshaft counterweights; reciprocating piston & conrod little end vibration which requires balance shafts to eliminate, and flywheel/engine rotational vibration (rocking) as a result of engine/flywheel energy exchange during the power and compression strokes.
The only way I can think of to get rid of the last one is to run a counter-rotating jackshaft geared off the crankshaft with an identical flywheel running in the opposite direction to counteract the rotational speed variations of the flywheel. A larger single flywheel will NOT help--the energy exchange must always be there and exists between the engine and flywheel. It can only be cancelled by an identical mass running the other way. Needless to say the two gears which drive this shaft must be capable of absorbing the impact loading that this second flywheel will absorb as the engine stores and retrieves power and compression energy alternately.
The linear vibration of the piston & conrod little end can be offset by balance shafts. Perhaps if the previously mentioned counter-rotating jackshaft with second flywheel is arranged on a line at 90 degrees to the cylinder axis ("beside" the cylinder), you can use these as your balance shafts to reduce weight & complexity. The centerline between the two shafts won't jive with the cylinder axis, but can be made close enough that it will help, and is simpler/cheaper/lighter than two correctly located balance shafts plus one counter-rotating jackshaft for the second flywheel running, say, underneath the crankshaft.
Now that I think about it, perhaps you could have two properly located balance shafts, and use the one that runs opposite to the crankshaft rotation to drive the other flywheel. (Oh yeah, the gears for said multi-purpose shaft must also be rather substantial!)
Alternately, a single-cylinder opposed piston layout can be used (no cylinder head, a crankshaft at either end of the cylinder with two pistons meeting in the middle to form the combustion chamber). With the two crankshafts synchronized by a timing drivetrain to counter-rotate, each having an identical flywheel, plus identical reciprocating masses, and properly balanced crankpin/conrod rotating masses, these engines can be made to run extremely smoothly even as single cylinder units. They also feature piston operated transfer and exhaust ports at opposite ends of the lung for excellent scavenging.
Just some thoughts,
PW