Thread: Constant Volume Combustion Engine (6-Stroke Engine)

now then my honda mind just goes into overdrive. this means that with this system and some modification of the design we can not only get different timings for the pistons. Can we also get VARYING strokes, if the "piston cam" for lack of a better word were to have different lobe shapes. at lower rpm's, have longer stroke and then switch to shorter stroke as rpms' climb?

addendum:i hereby coin the term Piston VTEC
hahaa

The people talking about cylinder deactivation, that's not how it works. imagine.. if you closed off all valves while it's at the top, you'd stop the engine.

It's true Caddies have been doing this since the 70's. the V-8-6-4. What it'll do is full open the exhaust valves, and close the intake valves. it's still a drag on the engine, (compared to a 4/6 cylinder made that way) because obviously it still has to pump that piston. but it's not that much of a drag, and it's more fuel efficient.

Still, not as fuel efficient as having a smaller, less powerful engine, though.


I do like Chrysler's new 300c. it supposedly has a 300 hp v-8 that features the cylinder deactivation. I'm still not so sure about it though... more features simply means more failure points.

sorry to nitpick- but coming straight from a thermo-lecture..... isnt it called isochoric rather than isovolumetric?

isnt there a 12 cylinder mercedes-benz that shuts off 6 cylinders at idle?

Originally Posted by chut

don't forget the "vidphone" did you ever read "safe at any speed" by Larry Niven

I saw a video phone at work the other day. I almost asked to have it.

Originally Posted by fluffy2097

I saw a video phone at work the other day. I almost asked to have it.

I have a video phone on my desk. Completely useless.

Originally Posted by nzKAOSnz

sorry to nitpick- but coming straight from a thermo-lecture..... isnt it called isochoric rather than isovolumetric?

i doubt most of the people reading that thing are going to have a degree in mechanical engineering... but, then again, i doubt they know what iso-anything will mean

to answer your question, yes it would be isochoric

~mike

Originally Posted by Suprapc

VTEC engages a second longer duration camshaft. <- from my understanding. Cadillac shuts down cylinder on its North star engines by no longer actuating the valves. Don't know about Honda.

The only Cadillac Northstar that shuts down cylinders for mileage is the V12 Cien concept. I think the Northstar will shut down one bank if the engine starts overheating, it supposedly alternates banks to keep operating temps down. In theory, you can drive the car with absolutely no coolant in it. (Not recommended)

Just to clarify, VTEC doesn't engage a second camshaft. THe camshaft has a low RPM and high RPM lobe for each valve (basically). The high RPM lobe normally just pushes a follower, but at high RPM, oil pressure pushes a metal pin through the follower and connects it to the valves, thus giving them higher left when needed.

Hmm... These Guys can explain it better. Check the links at the bottom if you want more detail. It's a nice technology, but I'd prefer an infinitely-variable system. There are some new engines that are close to being in (general) production that use solenoids to open and close the valves. I seem to remember reading about a diesel engine using hydraulic valve activation.

Since we're on the topic of high-tech drivetrain, I love this article.

With trickle-down theory, everything that happens in F1, eventually reaches us lowly commuters. Look at Disc brakes, ABS, Fuel Injection, Macpherson Struts, and even car computers!

Cheers,

Kris

This is what my dad had to say on the subject after taking a look at the link. I mentioned this to him when we drove over to kragen to pick up an oil sending unit for his 78 truck.

Actually, this is still a four stroke cycle engine, they're just calling the dwell times at TDC (combustion at constant volume) a separate stroke, and the dwell time at BDC (low pressure exhaust) a separate stroke. However, it is still a variation on a four-stroke cycle using a cammed crankshaft rather than a connecting rod-crank system. By the way, the steam engine developed by James Watt (invented in the 1700's) used an epicyclic drive system rather than a crankshaft (which would have been far simpler) because the crankshaft concept was patented by another individual. Replacing the crankshaft with another item (that performs a similar function) is not new.

The Ducati concept looks interesting, how do they handle piston float at high rpm? The lack of a connected crank introduces the possibility of the piston and crank/cam separating at high speeds, unless mechanically coupled. Ducati overcame this issue a long time ago with a valve train that did not use lifters, called the desmodronic drive (they called it a desmo-drive). The valves used rollers and the cam captured the rollers to provide mechanical coupling to open and close the valves, no spring return necessary. Maybe they are using a similar system here. Ducati is an innovator!

He's right, though. I dont see how it would handle the piston floating. at low RPM, you could pressurize the cylinder and it would drop it down...