Balancing shaft?

[Dsm91dsm]

Just curious..whats the difference with the Balance Shaft in the car,as opposed to not in the car?

 

[delta448]

The balance shafts are designed to quell the vibrations from the engine. They have counterweights offsetting each other and the crankshaft and are perfectly out-of-phase with the rotating assembly, which dampens the vibrations inside the engine.

If you don't mind the extra vibration, it is recommended that the B-shafts be eliminated. Most DSMers don't mind trading the smooth engine operation for a little more peace of mind. Proper balancing of the rotating assembly when doing an engine build can really minimize the added roughness of not having the B-shafts.

The rear B-shaft is connected to the oil pump which is driven by the timing belt, and there is another belt connected which drives the front shaft. This front balance shaft belt can fail and become entangled in the timing belt causing it to also fail. There have also been instances where the B-shaft bearings fail and lock up the shafts, and usually that causes the engine to jump timing and bend valves. A balance shaft eliminator kit (BSE or BSEK) contains a short stubby shaft to connect to the oil pump and replace the rear shaft, new bearings to block the oil passages to the front shaft and a plug to fill the hole where the front shaft used to be.

FFWD Connection - Race Injuns That Will Freeze Your Brain

 

[TunaTalon]

Proper balancing of the rotating assemby when doing an engine build can really minimize the added roughness of not having the B-shafts.

The 4G63 engine has balance shafts to cancel second order harmonic vibrations due to the velocity differences between the pistons. The piston going up does not exactly balance the piston going down because of the geometry.

Balancing the rotating assembly has no effect on second order harmonics. Balance shafts have no effect on the balance of the rotating assembly. The crankshaft and pistons are at the base frequency of the engine so that there is no way possible for them to compensate for the second order vibrations at two times the base frequency.

For more than you really want to know about vibrations due to piston dynamics please see http://www.kidzuku.com/StrokeOrNot.pdf.

 

[Defiant]

Mitsubishi copyrighted them as "Silent Shafts", and licensed them to Porsche for the 944 engine, and others.

 

[knochgoon24]

Mitsubishi copyrighted them as "Silent Shafts", and licensed them to Porsche for the 944 engine, and others.

Sounds like a mod for James Bond's car.

 

[TunaTalon]

Mitsubishi copyrighted them as "Silent Shafts", and licensed them to Porsche for the 944 engine, and others.

That jogged an old bit of 4G63 Intellectual Property history. But better to comment in another thread:

http://www.dsmtuners.com/forums/hangout/304026-counterfeiting-copyright-trespass.html#post151578315

 

[delta448]

Maurice, I didn't intend to mislead. I must be a bit mis-informed.

I'm both confused and intrigued by your post. I've read most of the paper (thesis?) you posted, some very interesting stuff you choose to write about.

Would you explain in simpler terms pardoning my ignorance, I'm afraid I don't follow your logic very well, in particular about the imbalance of pistons due to differing velocities. Is the crank centerline offset from the bore centers (you mention geometry) or what is the reasoning?

The 4G63 engine has balance shafts to cancel second order harmonic vibrations due to the velocity differences between the pistons. The piston going up does not exactly balance the piston going down because of the geometry.

Do you have any web links or published works you can direct me to that would help me understand better?

Please correct my misled notions, I honestly really want to understand. I'm sure I won't be the only one who is confused by your post and wants to learn more.

I assumed that a perfectly balanced rotating assembly would eliminate the oscillating forces applied to the block and remove the majority of vibration. You mentioned second order harmonics, what do you mean? Were you speaking of some sort of inherent resonant frequency? Related to engine configuration, or related to 4 stroke cycle, or...?

Balance shafts have no effect on the balance of the rotating assembly.

With all due respect, maybe they don't internally balance the rotating assembly, but I'm pretty sure that they do help balance it "externally" (using the term loosely) as I'd assume the harmonic damper does also.

Mind if I ask where you aquired the base of your umm.. "wisdom" ...for lack of a better word? Are you a professional or Mech E, or are you self taught? Either way you'll in the least have my full attention with your reply.

 

[TunaTalon]

Zack,
Thank you. That was an example of intellectual challenging without flaming that led me to join this site after years of researching how to make my Talon more like my Hemi powered 1948 Plymouth without losing the DSM driving experience while driving hard.

If you don’t mind, (Ok even if you do mind) I will respond one point at a time as if I were process driven.

Maurice, I didn't intend to mislead. I must be a bit mis-informed.

I'm both confused and intrigued by your post. I've read most of the paper (thesis?) you posted, some very interesting stuff you choose to write about.

I think of it as a white paper and tried to either confirm or challenge the conventional thinking. I am not trying to mis-lead, just inform.

Would you explain in simpler terms pardoning my ignorance, I'm afraid I don't follow your logic very well, in particular about the imbalance of pistons due to differing velocities. Is the crank centerline offset from the bore centers (you mention geometry) or what is the reasoning?

Ignorance is not an insult. It is just a word for things that you don’t know yet. When I started research into the StrokeOrNot document I shared your state of Ignorance. That’s why I tried to relieve my ignorance with knowledge.

Do you have any web links or published works you can direct me to that would help me understand better?

The StrokeOrNot document is fully referenced. For example the equations to find the velocity profiles are given in reference 17 (Techno’s) Appendix A lists all formula use in the creation of the chart. If no reference is given then the I am responsible for the derivation and the basis of the derivation is given.

Not said in the document is that I found multiple sources of the basic equations and compared different equations to make sure that there was a consensus. Then I did a seat-of the-pants analysis to make sure that results passed the smell test.

Please correct my misled notions, I honestly really want to understand. I'm sure I won't be the only one who is confused by your post and wants to learn more.

Back when I was working every day I was proud of my own confusion. Confusion is a sure sign of the creative process at work. Show me a person who is not confused and I will show you a person who will have no new thoughts.

I assumed that a perfectly balanced rotating assembly would eliminate the oscillating forces applied to the block and remove the majority of vibration. You mentioned second order harmonics, what do you mean? Were you speaking of some sort of inherent resonant frequency? Related to engine configuration, or related to 4 stroke cycle, or...?

You are right that a perfectly balanced rotating assembly will eliminate the oscillating forces at the frequency of the rotation. For example at 6000 RPM any static imbalance will cause a vibration at 100 Hz. (6000 RPM/ 60 secs/min) I paid hard earned money to get my Talon engine’s rotating assembly balanced.

Ah but here’s the rub. The balance shafts rotate at two times the engine RPM, because second order harmonics are vibrations that are at two times the base frequency of the engine. When I started drafting the document I thought (like you?) that for each pair of pistons the piston going up exactly balanced the piston going down because they were the same weight. Wrong.

Piston forces are a function of weight and velocity. If the rod ratio is very long then is all is well and the forces balance perfectly. But for real rod ratios piston velocities are different at the top of the stroke and the bottom of the stroke. See Figure 16, the velocity at the top of the stroke is about two times the velocity at the bottom of the stroke.

This is not a new or novel concept. Patent number 1,898,459 was issued to Edward Newcomb in 1933 for a means to balance 4 cylinder engines with rotating counterweights. Mr. Newcomb understood this before I was born and I think of Defiant as that nice young Moderator from Galt.

With all due respect, maybe they don't internally balance the rotating assembly, but I'm pretty sure that they do help balance it "externally" (using the term loosely) as I'd assume the harmonic damper does also.

Ah yes the harmonic dampener. That’s another story and way beyond the scope of StrokeOrNot.pdf or this post dinner post. (Post dinner post? That made sense when I typed it.)

Mind if I ask where you aquired the base of your umm.. "wisdom" ...for lack of a better word? Are you a professional or Mech E, or are you self taught? Either way you'll in the least have my full attention with your reply.

In my first post on this site I identified myself as a “retired hillbilly philosopher”. I’m afraid that my work must stand on its own merit (or lack thereof) That’s why the document is fully referenced. There were a few equations that I derived such as the side loading values. You just can’t trust anyone anymore. But politics are banned here.

If you still feel the need to “check me out” then please spend a few minutes on Kidzuku Home. Just remember that in my world “self taught” is far, far from an insult.

 

[delta448]

If you still feel the need to "check me out" then please spend a few minutes on Kidzuku Home. Just remember that in my world "self taught" is far, far from an insult.

No it's not that at all. No insult was ever intended. I was just curious about the source of all the information in your paper. I think that self-taught is the best way to learn -from first hand experience and not from a textbook. I consider myself to be self-taught. I've certainly made enough mistakes to prove it.