Balancing a three-cylinder in-line engine

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

Hi, try Taylor's "Internal Combustion Engine in Theory and Practice", or Thomson (Thompson??) "Fundamentals of Engine Balancing". Taylor seems best though.

There's a whole thread on this is if you search for engine balance or  look at Thread404-23811

Cheers

Greg Locock

A bit late! In Europe, GM market 975cc engined7 saloon as CORSA 12Valve. this is a three cylinder, in-line engine. There are DIY handbooks with loads of tecnichal info. A publishing co sells a popular handbook under the group title of [Haynes Manuals]. Alternatively, try GM!

I looked at the other thread Greg linked.I think the Geo was a rebadged Suzuki,Holden also rebadged them in Australia.

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??

I'll take a stab at it, and Greg can fill in the blanks when he next appears.

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.)

I came across the Charade engine when it was used in the BL Technology ECV3 research car - http://dspace.dial.pipex.com/town/way/yuw18/austin-rover/, look down at research vehicles, then the ECV cars.

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

I guess things have changed.  We covered engine balancing in our second year of school.  I remember being told that a three cylinder engine was inherently balanced and a four cylinder was darn tough to balance.  Detroit Diesel made a three cylinder 3-53 series that we used for years and it was very 'smooth.'  As I remember, chapter 7 of Charlie Mischke's book "Elements of Mechanical Analysis" covers this subject in depth.  Dig out your vector analysis book and substitue "calculator" where he says "slide rule."  You can look up what a slide rule is later.

I think your book may have been referring to the second order (and upwards) excitation from the L/r ratio, which, as you say, makes a 4 in line engine a very nasty piece of work. I3 and I6 engines are happily free of that particular issue, as it is resolved internally.

Cheers

Greg Locock

Any bikers out there know how the BSA and Triumph triples of the '70s were balanced?
By the way, I think there's a year 2000 SAE paper on 3-cyl balancing. I'll get back with the number.

I don't know how the Triumphs were balanced,but they were smooth and very easy to over rev.Laverda gave up on the 120deg crank and went for 180deg in later models.

The early GMC inline motors used a balance shaft,but I'm not sure which models you are refering to iaguy.

The three cylinder Suzuki engine found in the Sprint and Metro are balanced "as is" or so I'm told as I've never had the chance to do one.

The three cylinder BSA engine needs bob weights though.
The Perkins and Triumph engines also need bobweights.

Hope this helps.


Jon

There's an SAE paper that may help.....
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