Balancing

Flyer-4

Different methods of balancing:

In practice, different methods are used to balance rotating parts to its desired rating. We show you, what methods are used, and how they work…

Our examples are related to engine parts. However the operation mode is 100% transferable to all other rotating parts in industry (engine-anchor in electric drives, fan wheels and so forth).

Balancing – one level:

Is used for rotors in disc form (flywheels, belt pulleys, fans and so on)

Balancing – two levels:

For shafts and rotors with two bearings (in simple terms). The different methods of balancing and its explanation, see next paragraph.

In assembled state:

The ultimate treatment of every crank drive! Even if shaft and pulley are balanced to zero, it is possible, that the crank drive still has an imbalance. Find out, why 0 * 0 is not equal to zero.


Balancing in one level

The effect of the imbalance has to be shown at the example of a flywheel. Imagine, the disc is mounted on a free-moving axis.
To simulate the imbalance we mount a screw or something else like a magnet on one side of the disc.
By the force of gravity, the position at which the bolt or the weight is attached to the disc, will swing to the bottom, facing the ground. That is called a static imbalance.
In order to compensate this imbalance, we can remove the screw (mass ablate) or attach a equal wight on the opposite (180 °). Thus, our disc would be balanced again. A disc can be balanced without being set in motion by an external force.

In practice, however, nobody balance with a static method, because there are measuring inaccuracies due to frictional losses! In the dynamic method (in motion), these resistances are neglected. Modern electronics are capable to compensate even clamping errors! A big advantage over the simple static balancing.

Balancing in two levels

Lets take a look to a shaft which is mounted so that it can rotate about its own axis. The unbalance is simulated with a mass which is attached to the shaft. At first only on one side (left).
By the force of gravity, the side with the wight moves down. Thus result is a static imbalance. This can be solved even without rotation when the weight is removed or a equal weight is attached to the opposite.
The unbalance is compensated by attaching the same weight only at a different “level”. The shaft will not move on a bearing block because the weights are cancel each other.
The statically balanced state changes, when the shaft is brought into rotation. Starting at a low speed centrifugal forces work on the unbalance weights and brings the shaft in a so-called swash movement. We have two levels now, therefore we have to balance in two levels!

 


Balancing in mounted state

with master weights

Master weights are needed to simulate the masses of the pistons and con-rods.
This balancing method is only used with unsymmetrical crankshafts. This means V-engines, e.g. V5, V6, V8. In-line engines don’t need master weights.
The explanation is relatively simple. In a 4-cylinder engine the crankshaft rod journals and cheeks are always at 180° counterpart. That means, the masses are cancel each other. On a V-crankshaft the arrangement is not 180° – unfortunately we can not show you a Visualization, but we are working on it.

In mounted state

Shown here is a flywheel in completely mounted state.
belt drive + crank shaft + flywheel + clutch
Balanced this way and well assembled, the engine runs like clockwork.
If you balance two rotors to zero and then fit it together, the result will be an imbalance. In this case, the fitting tolerance represents the master problem.

By assembling a flywheel on a crankshaft you need some tolerance between the both parts, otherwise a correct fitting would be impossible.
This tolerance is called “eccentricity”. With too much tolerance it is possible, that the flywheel is wobbling around the crankshaft.
To avoid this situation it is necessary to balance the assembled device. We set a check mark to the right position, to avoid incorrect assembly.
On the picture at the right side, you can see the two base imbalances, showing to the top.
The balanced package has to be assembled in the same position as it was balanced. If the disc is mounted in a wrong position (see the picture on the right side), the result is a new imbalance and all desired effects are lost.
To secure a correct assembly of the package, we can set a adjust pin on the flywheel. This solution is standard in racing engines.