Discussion
I'm researching a bit so bare with me https://www.pistonheads.com/gassing/imgs/12.gif
I understand that the mass of the flywheel maintains the momentum of the engine and has something to do with torque and affects HP.
Is it just the mass/weight of the flywheel of does the diameter have much bearing on it at all?
I understand that the mass of the flywheel maintains the momentum of the engine and has something to do with torque and affects HP.
Is it just the mass/weight of the flywheel of does the diameter have much bearing on it at all?
See the Physics section of https://en.wikipedia.org/wiki/Flywheel.
As per replies above.
Just take it to an extreme in your own mind: imagine two flywheels of the same weight that you’re going to turn with a hand crank. One is 20cm in diameter, the other is 2000cm in diameter with almost all its mass at the outer edge. With the larger diameter flywheel you’ve less mechanical advantage to get it turning (accelerating).
From what I remember, in a car a lightened flywheel adds no power at all, but as with lighter wheels, it allows a higher rate of acceleration.
Just take it to an extreme in your own mind: imagine two flywheels of the same weight that you’re going to turn with a hand crank. One is 20cm in diameter, the other is 2000cm in diameter with almost all its mass at the outer edge. With the larger diameter flywheel you’ve less mechanical advantage to get it turning (accelerating).
From what I remember, in a car a lightened flywheel adds no power at all, but as with lighter wheels, it allows a higher rate of acceleration.
Edited by Tony1963 on Wednesday 16th January 06:09
it is not solely the mass, or diameter, but at what diameter the mass is that dictates the effect of a flywheel - the property of interest is moment of inertia or MOI for short. To fully get your head around what a flywheel is doing you have to understand it from the point of view of torque transfer and energy storage.
Without getting too physic-sy, internal combustion engine torque output is not smooth, it is a series of pulses as each cylinder fires. By fitting a flywheel, the acceleration experienced by the drivetrain is smoothed out, because the flywheel requires a torque reaction to accelerate/decelerate due to storing energy. Higher MOI flywheel will accelerate less for a given torque pulse (stored energy is the same, but speed change to achieve that is lower), and will decelerate more slowly when there is no torque pulse (it delivers its stored energy to the driveline, but by having higher MOI it doesn't decelerate as much to deliver the same energy), so maintains a smoother speed/torque trace.
Beyond a point, increasing MOI just has the effect of adding non-rotating mass to the vehicle as there is additional torque required to accelerate the flywheel, and engine speed doesn't drop as quickly as the flywheel stores energy.
Without getting too physic-sy, internal combustion engine torque output is not smooth, it is a series of pulses as each cylinder fires. By fitting a flywheel, the acceleration experienced by the drivetrain is smoothed out, because the flywheel requires a torque reaction to accelerate/decelerate due to storing energy. Higher MOI flywheel will accelerate less for a given torque pulse (stored energy is the same, but speed change to achieve that is lower), and will decelerate more slowly when there is no torque pulse (it delivers its stored energy to the driveline, but by having higher MOI it doesn't decelerate as much to deliver the same energy), so maintains a smoother speed/torque trace.
Beyond a point, increasing MOI just has the effect of adding non-rotating mass to the vehicle as there is additional torque required to accelerate the flywheel, and engine speed doesn't drop as quickly as the flywheel stores energy.
Edited by NotBenny on Wednesday 16th January 09:26
doubble99 said:
Wow, i feels like a proper noob now ??
OK, from that i might have a days worth of measuring and weighing to ensure i can get my calculations spot on.
Thanks.
what are trying to achieve? MOI can't really be "measured" by weighing and finding distances of an object, but can be inferred from experiment. If you have an object with uniform shape and made of 1 material you can do it from calculation, but otherwise you'll need to accurately model it in CAD, or find it experimentally.OK, from that i might have a days worth of measuring and weighing to ensure i can get my calculations spot on.
Thanks.
I have a thread on another forum. Don't know if it contents anything that will be of use?
Flywheel weights - MOI- What is it all worth?
http://speedtalk.com/forum/viewtopic.php?f=1&t...
Stan
Flywheel weights - MOI- What is it all worth?
http://speedtalk.com/forum/viewtopic.php?f=1&t...
Stan
NotBenny said:
what are trying to achieve? MOI can't really be "measured" by weighing and finding distances of an object, but can be inferred from experiment. If you have an object with uniform shape and made of 1 material you can do it from calculation, but otherwise you'll need to accurately model it in CAD, or find it experimentally.
I want to do a gearbox conversion, Leyland LT77 to a ZF GS6-37DZ, the gear ratio's leave a little to be desired but they are close enough.The flywheel housing will let me do a bit more than I first thought and it will be more about designing an adaptor plate and then of course the flywheel, it seems that the Rover uses a 9" clutch where as the BMW runs a 7" clutch, it will mostly come down to the spigot depth inside the bellhousing but it is looking like I could use a flex plate for the ring gear and a top hat style flywheel to marry the gearbox to the crank shaft?
Kind of my reason for asking about the weighting of the flywheel, it's for an off roader so not exactly a high revving drift car but it does need to work.
doubble99 said:
Kind of my reason for asking about the weighting of the flywheel, it's for an off roader so not exactly a high revving drift car but it does need to work.
An off-roader isn't the place for a light flywheel IMO (unless you are talking about racing on a loose surface rather than climbing rocks etc). You want a very flexible engine, happy pulling down to low RPM.If you want to measure the inertia of your existing flywheel, you need to build a Trifilar pendulum (often called a Trifilar Table).
Here's how they did it in 1962: TriFilar_Pendulum_US_Military
Slightly more modern take on it: TrifilarPendulumYouTube
Here's how they did it in 1962: TriFilar_Pendulum_US_Military
Slightly more modern take on it: TrifilarPendulumYouTube
After quite a lot of reading and looking at the double disc clutches I think that there is a real possibility that it could make a lot of the measuring up easier, but then I look at the prices, typically €1500 for just a clutch :-0 and it isn't looking viable, especially on the back of a Land Rover 200Tdi engine that probably puts out less than 110HP.
It is certainly an interesting topic and I will have to buy the chosen gearbox just so I can get the dimensions 100% when sat side by side next to the LT77.
I'm certainly not interested in an engine swap as I like the agricultural charm but I really would like the extra gear on the motorway and the much lower 1st gear of the GS6.
It is certainly an interesting topic and I will have to buy the chosen gearbox just so I can get the dimensions 100% when sat side by side next to the LT77.
I'm certainly not interested in an engine swap as I like the agricultural charm but I really would like the extra gear on the motorway and the much lower 1st gear of the GS6.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff