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Old 01-28-2013, 10:38 AM   #1 (permalink)
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New concept variable displacement??

I know there must be at least 5 automotive engineers monitoring our threads here so here is a thought for you.
Honda I believe sucessfully breached the electronic valve issue delving into variable valve timing.
Has there been an atempt to get this next step of variable engine displacement?
An example would be a 90 degree V6 where 2 cylinders are 4" and 4 are 2.5".
utilizing cylinder cut out and injector deactivation with all cylinders @ same stroke length The torque could be doubled for acceleration then dropped for cruising speeds and economy.
couple that to a hybrid with regen and electric boosters like formula one uses.
It could teach todays sports cars a nasty little lesson while providing 50+mpg???????
Not magic power just better utilization of it, with much less waste!

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Old 01-28-2013, 11:55 AM   #2 (permalink)
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...balancing "nightmare" trying to sling different sized/weighted pistons up & down, not to mention the vastly different MEP values from the two different piston/cylinder volumes.
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Old 01-28-2013, 12:57 PM   #3 (permalink)
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Does this question need an engineer?

The only degrees I have are my temperature, and a buddy tried to fly this idea past me. I raised the same questions you did: how in the world would you balance it? It doesn't take advanced edumecationing to know this would be a dog's breakfast.

I put it to my friend: why not just make all the cylinders work as well as you can possibly make them? Dropping out a couple of jugs when you don't need them is well and good, but mixing cylinder sizes in one engine feels like creating a problem for the intellectual challenge of then fixing it.

SAAB had a design a long time ago for a variable compression engine; one side of the top end was hinged from the bottom end, and a hydraulic servo would move the top up and down to bigger- and smallerize the combustion chamber as necessary.

You'll notice that SAAB didn't follow up on it, instead spending their time developing their brilliant turbo engines, a similarly effective and much more achievable method of making an engine behave as if it were two different mills. Those were the days.

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Old 01-28-2013, 02:12 PM   #4 (permalink)
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Unfortunately this thought moves in the opposite direction of the KISS mentality. While simple in theory, this is far too complex a design in reality to be implemented into the late stages of a fully matured technology.
Simplify, then add lightness.
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Old 01-28-2013, 04:19 PM   #5 (permalink)
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I really dont see a balance issue Ive seen old compressors where 1 cyl was ICE probbably 2 stroke other was compressed filter air.
It would make sense to perhaps do like a citroen v5 engine and drop 2 during low resistance.
I still like the big and small bucketts thought though.
1.9ci to 3.5ci just sounds rite.
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Old 01-28-2013, 06:26 PM   #6 (permalink)
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Variable compression ratios aren't new, there are scads of different designs for it, mostly by small companies that seem to have difficulty proving that they are worthwhile designs. Your idea seems similar to the Split Cycle engine, but I believe balance issues would be a problem with this particular implementation.

A year or two ago in my Automotive Engineering International magazine, I remember seeing that Honda had a functional prototype with variable compression that looked promising. I haven't heard much about it since, I imagine it's still in development.
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Old 01-28-2013, 06:37 PM   #7 (permalink)
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...the SAAB engine mechanically varied all four cylinders at once via a "tipping" head assembly as I vaguely recall.

...but, turbocharging accomplishes the same result much cheaper and controllably.

Last edited by gone-ot; 01-29-2013 at 03:50 PM..
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Old 01-29-2013, 01:07 PM   #8 (permalink)
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That one was wild.

But really... why go for difficult to implement variable displacement when variable trim turbos give you variable virtual displacement already for a fraction of the cost and complexity?
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Old 02-20-2013, 10:13 PM   #9 (permalink)
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Boy, maybe I am missing something on the variable displacement, but why not have a couple (or few) of v-twins connected by a clutch? It can't imagine balancing issues could be any worse than the current crop of cylinder deactivation autos. Valve shutoff is moot. The clutch should last quite a while. You could even make one of the engines a lot simpler than the other because it wouldn't have a very big affect on emissions because it would only run during acceleration.
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Old 02-21-2013, 10:46 AM   #10 (permalink)
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Old Tele man nailed it. Turbocharging is a simple way to do what you are asking.

As far as balance goes, it is amazing what can be made balanced. I recall that the Honda GP motorcycle engine for the RCV211 bike (2002-2006) was a V5 with three cylinders on the front bank and two on the rear. While Honda never released Bore X Stroke numbers, a few people found out through hearsay that the front cylinders each had a different displacement than the rear cylinders.
Honda RC211V - Wikipedia, the free encyclopedia

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