Engine Balancing

[Irwin]

I made a 2 cylinder diesel 90 degree V engine balancing. I found a simple equation to calculate the balanc weight.
My questions are the next:
1. Why is it necessary to balance the alternating forces from the masses? The forces from the burning processes are much higher!
2. Why do not we balance the alternating forces with "minimum finding method"? As I know the balance mass calculation concept comes form the highest alternating mass forces. We try to reduce this highest value! Why do not we try to decrease in all angle the forces from the balancing? This means a minimum finding! We will get total different balancemass!

That is all!

Irwin

 

[Wicsteve]

In general terms: The combustion process does not contribute to engine vibration. Remember that the explosion in the cylinder, for the most part, produces equal and opposite forces in all directions. Only the unbalanced forces and unbalanced moments as defined by the motion of the reciprocating masses contribute to the internal vibration of the engine.

Reduction in the mass of reciprocating forces should always be of concern regardless of the balance system used since mass reduction generally reduces the unbalanced moments and is effective in reducing the vibration at the secondary frequency (twice engine speed).

The selected angle between cylinders are also important in balancing recprocating masses. Some two cylinder engines were made with 60 degrees between cylinders to provide equal maximum forces in the up/down vs. horizontal directions.

 

[ivymike]

It's probably more accurate to say that combustion doesn't contribute to the vibration that you counteract with balancing.

Combustion will contribute to both noise and torque recoil (obviously).

 

[ansel]

I understand that honda auto engines are balanced at the factory(individually) and have been for some years. this was news to me and i thought it very unusual. does anyone know if this is unique, or what % of current production autos share this feature? bob b.

 

[GregLocock]

ansel:Virtually all normal automotive engines are individually factory balanced, for overall first order balance. This is typically a single plane operation for the complete engine, but many manufacturers balance the crankshaft beforehand as a two plane operation.

Typical balance wights for the final balance are washers on the flywheel, or tapered pins jammed into small holes on the crankshaft pulley. I suspect some people weld small plates on instead, as is done on driveshafts.

Wicsteve: Combustion does contribute to vibration, otherwise you couldn't hear it. Even if the internal pressure in the chamber was evenly spread it is then reacted via a series of paths with different stiffnesses and masses, the relative delays introduced by this causing a mismatch in the expected cancellation, and so you get a force and a vibration.







Cheers

Greg Locock

 

[patprimmer]

Greg
From your answer, I guess it is relativly simple to physicaly ballance the mass of the moveing parts, but the audible vibrations set up by combustion, are in a much higher frequency range than typical moveing mass induced vibration. Also, I expect that they are very variable (even in the one engine) in amplitude and frequency, depending on throttle position, engine speed, A/F ratio and ignition timeing, henceforth, ballancing to counteract is impossible, but design, shape and appropriate placement of mass might be effective in dampening the vibrations.
From, I must admit mainly anecdotal evidence, that is why Nissan use a curved surface (to match the profile of the bores) on the outside of their inline 6 engines, and carry the block well below the crankshaft centre line. I guess that is also the reason for considerable external ribbing on the same engine Regards
pat