Balancing a three-cylinder in-line engine
Balancing a three-cylinder in-line engine
(OP)
Hi,
I would like to know how a three-cylinder in-line IC engine is dynamically balanced.since we've faced this problem in the lab and I've heard it's currently used in the automotive industries.Is there any way to balance it and release vibration.
or refer me to a site or book.
thanks very much
epsilon
I would like to know how a three-cylinder in-line IC engine is dynamically balanced.since we've faced this problem in the lab and I've heard it's currently used in the automotive industries.Is there any way to balance it and release vibration.
or refer me to a site or book.
thanks very much
epsilon





RE: Balancing a three-cylinder in-line engine
RE: Balancing a three-cylinder in-line engine
Cheers
Greg Locock
RE: Balancing a three-cylinder in-line engine
RE: Balancing a three-cylinder in-line engine
The Daihatsu 3cyl used an engine speed balance shaft as Greg suggested,it had very large gears,which used to wear rapidly,an indication of the forces involved.But I have always puzzled over the layout of the shaft,this had two weights 180deg apart,timed to no1 cyl.I can't see how this can help with the balance of a 3cyl,any insights Greg??
RE: Balancing a three-cylinder in-line engine
A three cylinder engine, with the cylinders phased 120 deg apart, will have no vertical or horizontal shaking force, as the sliders will cancel each other out. Instead, it will have a pitching moment (and a yaw moment, if I'm not mistaken), as the acceleration-forces of the end cylinders will not precisely cancel each other. The 2-weight balance shaft, counter-rotating at engine speed, can generate opposing pitch and yaw moments. (I think it's counter-rotating, but that's just off the top of my head, so maybe someone can verify that for me.)
RE: Balancing a three-cylinder in-line engine
I was involved in this in my first real engineering assignment, a couple of years before I became an NVH engineer. Consequently I can remember very little about the engine mounts or the engine configuration.
Later on the same group designed and built the prototype K engine, which was a 3 cylinder, and installed it in a Metro (I think). By then I was in NVH and we had the job of finding out why it was so noisy, which is when we got to grips with the 3 cylinder first order moment problem, well described by ivymike. At the time deciding on engine mount locations and rates was a lot more hit and miss than it is today, particularly for front wheel drives. Having said that, I still wouldn't like to have to install a 3 cylinder if it didn't have a balancer shaft.
Yes I think the balance shaft should counter-rotate.
Incidentally the reason that they went 3 cylinder for the K (initially) was that we were in the middle of some oil crisis and fuel consumption was king. Somebody had done some work indicating that 400 cc was the ideal size for a cylinder, and we needed about 1300 cc. So we got three cylinders. Shame really, an opposed twin would have been a much better engine, and would have scaled nicely up to 2 and 3 litres.
Cheers
Greg Locock
RE: Balancing a three-cylinder in-line engine
RE: Balancing a three-cylinder in-line engine
Cheers
Greg Locock
RE: Balancing a three-cylinder in-line engine
By the way, I think there's a year 2000 SAE paper on 3-cyl balancing. I'll get back with the number.
RE: Balancing a three-cylinder in-line engine
The early GMC inline motors used a balance shaft,but I'm not sure which models you are refering to iaguy.
RE: Balancing a three-cylinder in-line engine
The three cylinder BSA engine needs bob weights though.
The Perkins and Triumph engines also need bobweights.
Hope this helps.
Jon
RE: Balancing a three-cylinder in-line engine
http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=2000-01-0601
Document Number: 2000-01-0601
Collection - Book Number: SP-1515
Title: A Study on the Balancing of the Three-Cylinder Engine wtih Balance Shaft