Flywheels are a good storage of kinetic energy

[Jones1987]

So, these things are baffling my mind. I understand they are a good storage of kinetic energy, and help keep momentum of motion.

What I cannot get my head around is, how are they started say within a car, also I assume once the engine is turning over, why is the flywheel needed, so what is the purpose of it?

This may sound really retarded to some people, but I just cannot picture how it comes into play. Any information or for someone to explain these questions would really clear this mess inside my head.

 

[mgb_phys]

In a car the flywheel is needed to turn the pistons around at the end of their stroke.
Picture a car piston engine (or a steam engine) when the fuel has burned and the piston pushed down to bottom where does the turning force come from to push it back up?

Without a flywheel the crank shaft would just sit there.
Some engines don't need a crankshaft flywheel because of the arrangment of the cylinders, this was BMW argument for why you should only have 6cylinder engines - when they only made 6cylinder cars, the same thing applies to boxer engines http://en.wikipedia.org/wiki/Flat_engine

 

[Jones1987]

Excellent, now I can see why they are used. I have been watching videos on youtube of little flywheel hot air engines and couldn't figure out, but pushing the piston back after the cycle make perfect sense. Now I think about the crank shaft I can see why it is needed.

Thanks for that, cleared a right mess in my head.

 

[xxChrisxx]

However on all cars, it doesn't matter if they have overlapping powerstrokes you should have a flywheel. As it acts as a buffer to smooth out power delivery. Which is good for both stresses and the 'feel' of an engine.

 

[Jones1987]

Yeah I was thinking about that last night, would you not get jolty motion without a flywheel. Once the main use was explained I think my brain just began to overflow with ideas of its uses, haha

 

[brewnog]

You would, yes. This is one reason (but not the main reason) that a high performance race engine (with very light flywheel) is a bugger to drive under normal road conditions.

 

[mgb_phys]

IIRC the only balanced engines without a flywheel (or balanced crankshaft) other than boxers are a straight 6 and V12?

 

[brewnog]

All the straight 6s and V12s I've ever dealt with have had a flywheel, although they are considered to be 'balanced' from a reciprocating mass point of view. They still need a flywheel for providing inertia to damp out transient effects and improve smoothness and driveability.

 

[xxChrisxx]

IIRC the only balanced engines without a flywheel (or balanced crankshaft) other than boxers are a straight 6 and V12?

You can technically run a I6 or V12 without a flywheel, but you will have a nasty driving experience.

Also you will also find both I6 and V12 cranks with couterwights, even though they are fully balanced as it reduced variations in bearing loads. racing engines won't have this, but road engines will.

 

[Bob S]

My car needs a flywheel to connect to the clutch plate and to the starter.

Bob S