Direct drive vs. geared flywheel?

[crueby]

Anyone ever do an engine with the flywheel geared up or down from the main crankshaft rather than directly on it? I think I've seen that done on traction engines. Seems like it would be a way to use a smaller flywheel but still get the benefits of a larger one, but maybe with side effects on ease of self-starting. Not sure how the physics of that would actually work out - anyone have some practical experience on the tradeoffs?

 

[MachineTom]

One reason and maybe the biggest reason you do not see geared flywheels is the inertia of the flywheel would require large gears to handle the load of each firing/filling of the cylinder. Expense, noise, wear add up to a bad design.

You can surely model a design with geared flywheels, since wear and expense are of little issue when building a model. I like gears, the last friction drive car I built had 14 gears, 4 wheel drive.

 

[glue-itcom]

Just been doing some more reading on geared flywheels and so found this forum page. The original gearing was done to overcome patent issues: 1781: Sun and planet gear – invented by Boulton and Watt to circumvent the crank patent as they adamantly opposed cross-licensing their condenser technology.

I have made a geared flywheel for an oscillating engine:


The issues/considerations:

1. gear noise is significant
   1. torque reversals as flywheel absorbs energy and then puts that energy back into moving the crank at a later point in the cycle
2. gears contribute to the inertia
3. gears need to be substantial
   1. balance between being strong enough and minimising losses - tooth to tooth shear
4. flywheel runs at a higher speed
   1. hence more windage losses
   2. more structural considerations

Some static images of the engine here, the gearing is more of a gimmick than anything else.

 

[TrainMaintainer]

Anyone ever do an engine with the flywheel geared up or down from the main crankshaft rather than directly on it? I think I've seen that done on traction engines. Seems like it would be a way to use a smaller flywheel but still get the benefits of a larger one, but maybe with side effects on ease of self-starting. Not sure how the physics of that would actually work out - anyone have some practical experience on the tradeoffs?

Functionally, at least, you do get this very thing with a number of diesel-electric locomotive engines. It's often advantageous to have the generator running at a higher RPM than the actual engine (electrical efficiency, higher frequency output, etc), so you do sometimes see the generator geared up from the crank speed. And since the mass of the generator's rotor can often exceed the mass of the actual engine flywheel, it does contribute to flywheel effect via the gearing.

I'm actually considering doing the same for a 5" gauge diesel-electric loco I have on the drawing board, since the alternator (actually 2 of them, rotors running on the same shaft but stators connected in series for twice the voltage) I want to use are ideally spun at about 2.5x the engine speed I'd like to have for maximum authenticity in terms of engine noise and exhaust note. But since it's going to have dual, counter-rotating crankshafts with 2 conrods per piston, anyway, it's only one more gear, right? ;-)

 

[Rdean33422]

This is a chain drive engine I built in 2020.
It was originally a gear drive.


Ray

 

[HMEL]

Anyone ever do an engine with the flywheel geared up or down from the main crankshaft rather than directly on it? I think I've seen that done on traction engines. Seems like it would be a way to use a smaller flywheel but still get the benefits of a larger one, but maybe with side effects on ease of self-starting. Not sure how the physics of that would actually work out - anyone have some practical experience on the tradeoffs?

Flywheels are used to store inertial energy to help balance engine vibration and force the crank past a dead center point. It smooths out the engine pulses. The amount of mass is calculated and will vary based on total mass of crank and other factors. For reliability purposes less gears the better. The older john deer tractors b model for instance the flywheel was mounted on the side and started with it. It was a two cylinder engine. However, some aircraft starters were started with a crank flywheel system and these were geared devices to obtain the high rpm. After starting the units were disconnected from the crank and the prop performed part of the function of the flywheel. The stored energy is a simple matter of mass and the rpm it spins at. And it does matter where the weight is on the wheel. Is it a smooth disk or one with the mass on the rim. And one of the critical design factors is the stress of this mass on the wheel itself. It has to be strong enough to stay together at the operating rpm.

 

[Steamchick]

Use of belt drives instead of gears can resolve issues of "resonance" - causing damaging gear wear, etc, - due to the compliance of belts (dynamic damping). Also it is good to have "Hunting" teeth - if using gears - or odd ratios of pulleys, sprockets, etc. for continuous linked drives. Simple ratios of flywheel to engine shaft are only used normally for cams, balance shafts, etc. that must be synchronised to the engine. An electric generator or turbine pump welcomes a high ratio from crank to operate at a suitable speed. - If the engine can handle the torque at lower speeds.
Very complex decisions (from calculations) on cars, etc. to achieve longevity.
K2

 

[TSutrina]

A belt is both a dampener and a spring. So there can be situations where in has the resonance near one of the machine's resonance. A directly connected flywheel lowers the resonance frequencies and the amplitude resulting. www.sandv.com › downloads › 0505swan.pdf

 

[Henry K]

I have seen quite a few videos on WW2 German ME109 fighters using geared flywheels on their Mercedes engines. I think they were also common on Rolls Royce Merlins. For your use, just design a twist out engagement mechanism as soon as the engine RPM exceeds the flywheel RPM. This is fairly simple to do.

 

[TSutrina]

Weight is a big problem with aircraft so they would use gears to reduce the weight of a flywheel, however; the quality of the gears would be much higher then likely the rest of the gears. This was the case for the gears in torpedoes where noise was an issue. Noise is produced by the same imperfections that would create vibrations.

 

[Henry K]

It is my impression that once the small (high speed) flywheel is disengaged from the aircraft engine no gears in this system are engaged with whatever noise they make. I any case, the unmuffled Mercedes or Rolls-Royce engine should be many times noisier than the gear train. In addition, the reality is that these gears are engaged for about 5-10 seconds in what will be a 2 to 6, or more hour flight. Remember these engines were used on British bombers flying to Germany and, hopefully, back. Finally, the pitch angle of gears can greatly reduce the gear noise. Think about the gears in a Hardinge lathe.