A three cylinder boxer engine

[ueberooo]

I have a pretty crude animation of an imagined three cylinder boxer engine. I don't know whether it's better posted under the general discussion topic or here, but I figure the readers here are more likely to get it to run and give feedback on whether such a crazy idea would be feasible.

All cylinders are 120 degrees out of phase and always balanced. The expanding circles denote a power stroke.

You can run the applet here:
[URL]http://ee.freeshell.org/boxer3cyl/animation.html[/url]

Or download the *.java source , compile: ( java *.java ) and run:
java Animation

My thoughts are the power output at the wheel wouldn't be as even/smooth as a 4 cylinder but it might have a nice character type of beat feel that some would fancy.

Are there other flaws or problems for a hypothetical horizontally opposed 3 cylinder engine?

 

[Rand]

they would need to be opposed to cancel the forces out?

 

[ueberooo]

No single pair is opposed (sum over two cylinders), but the sum of the three three cylinders (center of mass) remains a constant. The three kind of act as a pair.

 

[ctrcbob]

My thoughts are the power output at the wheel wouldn't be as even/smooth as a 4 cylinder but it might have a nice character type of beat feel that some would fancy.

Are there other flaws or problems for a hypothetical horizontally opposed 3 cylinder engine?

NOT AS EVEN/SMOOTH AS A FOUR CYLINDER?????? I'm glad you think a four cylinder is smooth. Every four I've ever seen, or listened to, is much rougher than a six, an eight and even a five (Volvo) or a three (Geo) (BMW K75 Motorcycle).

I tend to agree with you as to character because I once owned a 62 Buick Special V6. This was before Buick had offset crank pins on the 90 degree engine. Uneven firing, but I loved the sound. I used to say that it sounded more like a V8 than a six. A couple years later, they installed offset crank pins which gave the 90 degree V6 even firing. (Some brands even to today went to 60 degree cylinders so no need for any crank offset).

 

[4wheeldog]

I cannot get your animation to load. However, a 3 cyl radial (Which is what a 3 cyl "Boxer" amounts to....Is heavy, bulky and expensive for its power output.

Did you know that Henry Ford really wanted to build X8 motors, but his engineers finally made him realize that a V8 was much easier to manufacture?

 

[ueberooo]

I find 4 cyls pretty smooth, there's a power stroke going on at about any point in time, but I guess 8s and 6's are even smoother at lower rpms.

A 3 boxer probably would be very similar to a 3 cyl radial. But somewhat less bulky, because the cylinders are all lined up with each other; two on the left bank, one on the right, and crankshaft in the middle that runs perpendicular and divides the left and right bank ( like in a boxer 4, except with one cylinder missing). I like the sound of it, from what I've found on youtube .

Someone who is experienced building engines probably could take a regular 4, disconnect one cylinder, put a custom crankshaft where the cranks are 120 deg out of phase rather than 90, and fix the timing (camshaft) for the valves and spark plugs to work correctly, and he'd have a prototype. I wish I knew something about engine building

 

[Silk]

I would think the Commer TS3 with opposed pistons would be more correctly called a boxer. A 3 cyl engine is not in good balance, and some 3 cyl engines like the Diahatsu have a balance shaft. Laverda made their later 3 cyl engines with a 180 crank...4 cyl with one missing.

 

[Shannow]

Silk, was that the Jota ?

End two up, middle one down ?

I remember some road tests at the time and they were very very surprised at what was achieved with that arrangement...which is why I laughed when workmates were telling me about the advances in cross plane cranks for GP 4 cylinders.

 

[ueberooo]

Originally Posted By: Silk
I would think the Commer TS3 with opposed pistons would be more correctly called a boxer. A 3 cyl engine is not in good balance, and some 3 cyl engines like the Diahatsu have a balance shaft. Laverda made their later 3 cyl engines with a 180 crank...4 cyl with one missing.


You're completely right, I gather, after thinking more carefully about this. The TS3 would be the 3 cyl-boxer (with funny arrangement of two crankshafts and twice the pistons). Wiki points out this idea here would actually be more a V-3 (a Saab invention possibly) but with a 180 deg V angle:

Are (most correctly done) straight 3 cylinder engines naturally balanced enough not to require counterweight balances?

Back to the idea above... if you put all the cyls on one side (bank) you get a regular straight engine on its side, and you save space. Yet why didn't people turn straight 3's (or others) on their side for lower center of gravity advantages?

If you put the middle cylinder on the opposite side (V-3 180 degree), you make the engine larger and longer, but you get to reduce the length of the crankshaft and the distance between the cranks by staggering the cylinders along the width.

What are some decent 3 cylinder 1990s or 00's cars out there? The Laverda thing sounds funny/crazy; never heard of them before today!

 

[Shannow]

If you take a straight 6, it can be perfectly balanced, with no rocking couple.

A 3 can have the same balance, but will always have a rocking couple.

Diahatsu Charade was a biggie in Oz, and it did pretty well with it's three cylinders (IMO)...Smokey was prepared to chop a bank of the (Buick???) V-6, creating a slant 3 cylinder, with his heat exchangers and whatnot for the hot vapor cycle in the "V"...I find a 1.9-2.1L slant 3 somewhat appealing, in an odd sort of way.

 

[supercity]

Triumph 675.
A lot of tractors use I3 engines.

 

[Silk]

Originally Posted By: Shannow
was that the Jota ?
End two up, middle one down ?


Yes, there was trouble with the 120 crank breaking with the rocking couple, so they went to the 180, with the middle one down.

The Charade was a tough engine, I had a GTti which was a turbo dohc and a fast little hatch. A guy saw it parked in my shop and came in to have a look, as they are not common. He was a mechanic in a rally team that used them, they boosted them to 60psi and never lost an engine.

Back to motorcycles again, Honda made a 3 cyl 2 stroke, the MVX250, which had 2 cyls facing forward and one upright. They were prone to problems, seizing the rear cyl, I remember seeing a couple in bits I could've got cheap, but why get involved in a problem child?

 

[ueberooo]

I think some geo metros were 3 cylinders, as well as subaru justy's. I think the production of those ended late 90s and mid 90s.

I was wrong about he saabs having V-3's, some of their early cars had a V-4.
On their inline 4 engines, they slanted it slightly off the vertical so they could line up the transmission down the middle of the car or so. I drove a 900s briefly; nice engine until it developed coolant problems that went unattended.

Now if they only had tilted it 90 degrees to be horizontal, it would have a significantly lower CG, but it would cause problems because the driveshaft/crankshaft would be on either on the side of the car, or the rear of the engine compartment oriented like a transverse engine. Pobably hard to build a transmission around that.

 

[Cujet]

Originally Posted By: Shannow
If you take a straight 6, it can be perfectly balanced, with no rocking couple.


I drove a Volvo the other night with a wonderful Inline 6 turbo. I was the designated driver (I don't drink) and my passengers were drunk. The passenger placed the shifter in manual mode without my knowledge and downshifted to 3rd gear at 73MPH. The engine was running at 5000RPM and I never noticed it. Man is that thing a smooth engine! Eventually he told me and I placed it back in drive. Funny that the engine is so smooth at any RPM.

I absolutely love inline 6's.

 

[expat]

Originally Posted By: ueberooo
I think some geo metros were 3 cylinders, as well as subaru justy's. I think the production of those ended late 90s and mid 90s.

I was wrong about he saabs having V-3's, some of their early cars had a V-4.
On their inline 4 engines, they slanted it slightly off the vertical so they could line up the transmission down the middle of the car or so. I drove a 900s briefly; nice engine until it developed coolant problems that went unattended.

Now if they only had tilted it 90 degrees to be horizontal, it would have a significantly lower CG, but it would cause problems because the driveshaft/crankshaft would be on either on the side of the car, or the rear of the engine compartment oriented like a transverse engine. Pobably hard to build a transmission around that.




The Saab V4 was a Ford engine that replaced the Saab 3 cyl Two stroke engine.

The Slant 4 used by Saab was a design by Triumph in the U.K.
the idea of the 45 degree slant was so the Hood line could be kept low with the Tall OHC engine.
The drive train was not off-set

 

[ueberooo]

Thanks for the correction. Yes that 900s hatchback was aerodynamic, low sporty hood, and had lots of glass all around, great visibility and ergonomics and was great for road trips.