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Car Forum / Australian Car Forums / General Car Topics (Australian group) / March 2008Hondas V6 thats a 4 or a 3 Cylinder
Seen the new Hondas with diplacement on demand now being offered on the Accords. Est Econompy 10.5L/100 with active noise suppresion through the sound system when in 3 Cylinder mode. States have had them in the People movers for a while. Interesting having the remaining cylinders fucntion as air springs, Valves are shut / shutdown > Seen the new Hondas with diplacement on demand now being offered on > the Accords. [quoted text clipped - 3 lines] > Interesting having the remaining cylinders fucntion as air springs, > Valves are shut / shutdown It kinda makes sense to me. Although I'm not into Honda. I drive a near 2 tonne turbo diesel pickup truck that gets less than 10 l/litre 100/km, so it's not really interesting. "the_dawggie" <the_dawggie@hotmail.com> wrote in message news:ff174438-380a-4f63-b393- > I drive a near 2 tonne turbo diesel pickup truck that gets > less than 10 l/litre 100/km, so it's not really interesting. You drive a Hilux ute, and if it weighs near two tonne someone's stuck some lead ballast in it and not told you :) -- Regards, Noddy. > Seen the new Hondas with diplacement on demand now being offered on > the Accords. [quoted text clipped - 3 lines] > Interesting having the remaining cylinders fucntion as air springs, > Valves are shut / shutdown why leave the valves closed surely open valves would offer less resistance when they are not operating, or at least some sort of decompression Kev > > Seen the new Hondas with diplacement on demand now being offered on > > the Accords. [quoted text clipped - 9 lines] > > Kev You missed the "springs" bit. Some energy is used within the piston to compress the air inside. When the piston reaches TDC the air is at maximum pressure. As the piston descends again the energy used to compress the air is given back as it expands. This is actually pretty efficient because the only losses are the friction of the piston itelf, plus the loss of heat through the walls of the cylinder. If you pump air in and out you have add on top of that, the losses in the intake/exhaust system to pump air in and out, the loss of heat that goes out with the discharging air, plus the energy required to move the valves. Who really gives a sh.t - it's nothing more than gimmickry to impress the dull witted. In reality, a well designed engine attached to a well thought out driveline will do better. Or just buy a damn diesel.  SignatureVYBerlinaV8 -- Posted via a free Usenet account from http://www.teranews.com >>> Seen the new Hondas with diplacement on demand now being offered on >>> the Accords. [quoted text clipped - 15 lines] > efficient because the only losses are the friction of the piston > itelf, plus the loss of heat through the walls of the cylinder. Which is how a compression brake on a truck works, only in reverse but the compressed air is also bled off just after compression, which is where the noise comes from > If you pump air in and out you have add on top of that, the losses in > the intake/exhaust system to pump air in and out, the loss of heat > that goes out with the discharging air, plus the energy required to > move the valves. I understand that but a simple test, remove the spark plug from your mower and pull the cord, requires much less energy to turn the engine than with the plug in place maybe the resulting fart sound from the exhaust would put owners off Kev > >>> Seen the new Hondas with diplacement on demand now being offered on > >>> the Accords. [quoted text clipped - 34 lines] > > - Show quoted text - With the compression brake on the truck, because the air is compressed in the cylinder and then released to the atmosphere at Top Dead Centre at the point of highest pressure, it doesn't give the stored energy back to the engine. That's an important difference. The noise you hear results from the engine's kinetic energy being dissipated into the air and that's what gives the braking action. Also with the mower, yes it's harder to approach top dead centre by hand with the sparkplug in, but notice how it spins a bit when you get it past top dead centre. Thats the energy being returned to the system. The force required to approach top dead centre is significantly higher than with no spark plug, but the energy you use is given back when the piston passes top dead centre and the flywheel continues to turn as the air trapped inside pushes the piston back down. This effect is strongest in four stroke engines, unless the valves are not sealing properly. Now consider the Honda engine with say four cylinders operating and two just closed off. The two cylinders do not compress at the same time, so when one is requiring energy to compress the air, the other one is giving it back. Also the engine is running at more than 2000-3000RPM when it does this, so the energy is stored in and released from the flywheel inertia as the engine turns. The same principle applies with three cylinders shut off, but different cylinders. >With the compression brake on the truck, because the air is compressed >in the cylinder and then released to the atmosphere at Top Dead Centre [quoted text clipped - 22 lines] >The same principle applies with three cylinders shut off, but >different cylinders. Witness the Clae and Blaxland marine engines which were started by throwing the flywheel in the reverse direction to engine operation and bouncing the piston off the compression to reverse the rotation and start the engine. OzOne of the three twins I welcome you to Crackerbox Palace. > Also with the mower, yes it's harder to approach top dead centre by > hand with the sparkplug in, but notice how it spins a bit when you get > it past top dead centre. Thats the energy being returned to the > system. *Some* energy would be returned to the system. You can bet any money you like that the amount of energy released by the expanding air would be less (and considerably so) than the effort required to compress it in the first place. > Now consider the Honda engine with say four cylinders operating and > two just closed off. The two cylinders do not compress at the same > time, so when one is requiring energy to compress the air, the other > one is giving it back. Also the engine is running at more than > 2000-3000RPM when it does this, so the energy is stored in and > released from the flywheel inertia as the engine turns. It's a V6 engine I beleive, so unless Honda has come up with a world first method of fixing the inherrant balance issues associated with these engines shutting down cylinders is going to achive very little of anything, and probably create problems in other areas. Namely piston ring seal longevity. Piston rings require the gas load of a firing mixture to keep them firmly bed against their bores, and running a cylinder for extended periods without this load will do absolutely nothing for ring life. I'd also have to wonder about your quoted rpm figures as I would have thought to cylinder shutdown would be at cruising speeds, and unless they've geared the thing incredibly low 3000rpm seems a tad high. > The same principle applies with three cylinders shut off, but different > cylinders. If anyone *really* wants to see how well this will work, just pull a couple of plug leads off your V6 powered anything and go for a cruise :) -- Regards, Noddy. > > Also with the mower, yes it's harder to approach top dead centre by > > hand with the sparkplug in, but notice how it spins a bit when you get [quoted text clipped - 37 lines] > Regards, > Noddy. I almost didn't mention numbers for the RPM, because I knew someone would point out that it was wrong. The actual number doesn't matter - the point being it's a lot faster than turning it by hand. I'm guessing this engine would have a 60deg V angle for good balance. Don't judge it by those V8-with-two-cylinders-missing Buick monstrosities. Honda's system would not be the same as pulling spark plug leads off a conventional engine because in the conventional engine the valves are still operating and removing all of the stored compression energy of the non functioning cylinder. Yes not all the energy is returned in the closed off case - that's because of friction, leakage and entropy, but when closed, the cylinder functions like an air spring and shouldn't lose any more energy than when it is operating. Absent in that case also is the force needed to open and close the valves against their springs, which can be considerable. I don't think anyone believes that this would be as efficient at cruise as, say a real 4 cyl engine, but it is an interesting way of getting better efficiency at part throttle cruise from a multi cylinder engine. The issue as suggested is keeping the whole thing balanced and smooth enough to be transparent to the driver. I have no idea though how Honda have designed this system to work, but I know cylinder deactivation was first proposed over twenty years ago and tried by GM in a Cadillac(http://en.wikipedia.org/wiki/ Cylinder_deactivation#Cadillac_L62_V8-6-4), which was a bit of a flop. Other (better?) attempts were made by Mitsubishi and Daimler Chrysler. It's taken this long for someone else to make it work well enough and for fuel costs to be enough of an issue to try it again. Given their history of boldness when it comes to "out there" ideas I'm not surprised that this came from Honda. I'll be watching with interest to see whether it works or not. Not all of their ideas have, but that doesn't seem to stop them. > I almost didn't mention numbers for the RPM, because I knew someone > would point out that it was wrong. The actual number doesn't matter - > the point being it's a lot faster than turning it by hand. I'm > guessing this engine would have a 60deg V angle for good balance. > Don't judge it by those V8-with-two-cylinders-missing Buick > monstrosities. I wasn't, as it's the 60 degree V6's that have inherrant balance issues. The 90 degree jobs are fine :) > Honda's system would not be the same as pulling spark plug leads off a > conventional engine because in the conventional engine the valves are [quoted text clipped - 3 lines] > but when closed, the cylinder functions like an air spring and > shouldn't lose any more energy than when it is operating. Not quite. It'll always consume more energy in compressing the air than the compressed air gives back on expansion, and while that won't exactly be like driving a car with a couple of dead cylinders it won't be "free" either. Combined with the other loses (including the increased consumption of the firing cylinders as they need to do more work with 2 or 3 cylinders "out") one has to wonder just how much would be saved by not burning fuel in those cylinders. > Absent in that case also is the force needed to open and close the > valves against their springs, which can be considerable. They can be in certain cases, but not in your average OHC V6 I expect. They generally run very light springs. That's not to say that it doesn't cost power to run the valvetrain, but it's not huge by any stretch. > I don't think anyone believes that this would be as efficient at > cruise as, say a real 4 cyl engine, but it is an interesting way of > getting better efficiency at part throttle cruise from a multi > cylinder engine. The issue as suggested is keeping the whole thing > balanced and smooth enough to be transparent to the driver. Be interesting to see how they've gone about it, and I expect being Honda they'll have done a decent job. However, I'd also add that Honda are one of the most pedantic manufacturers on the planet, and the real interest (for me at least) would be what economy gains are to be had compared to the complexity of having the system in the first place. I'd be surprised if real world gains were more than 10%, and in such a case I'd *really* wonder why they bothered. Then again, in a lot of cases such "technology advances" are as much about sales gimmick wankery as they are about anything else. > I have no idea though how Honda have designed this system to work, but > I know cylinder deactivation was first proposed over twenty years ago > and tried by GM in a Cadillac(http://en.wikipedia.org/wiki/ If I remember correctly (I haven't looked at the wiki link as my browser is on the fritz at the moment), some (probably military during the war)played around with the idea of a hydraulic crankshaft coupling that would totally shut down banks of reciprocating assemblies, but I don't know how successful it was (obviously not terribly, or we'd be using it today). If they could get *that* idea working, as in completely shutting down half of a V8 engine so the front 4 cylinders remained totally motionless, that would be something. > Given their history of boldness when it comes to "out there" ideas I'm not > surprised that this came from Honda. I'll be watching with interest to > see whether it works or not. Not all of their ideas have, but that > doesn't seem to stop them. I was a service & parts manager of a Melbourne dealership at the time when the NSX first came out, and as the dealership I worked for was one of the more "up-market" few that was going to get them I was sent packing to Japan for a week (along with a few other such managers from around the country) for a familiarisation course which included a tour of the factory to see the things being made, a few drives around their test track and some indoctrination into the ways of all things Honda (and, in particular, the NSX). Before I left for that trip I knew Honda pretty well, and had always believed (as I do now) that they made a pretty good car. I also had to deal with them at a "head office" level and knew how "interesting" they could be. However, nothing opened my eyes as to how incredibly far *up* themselves they really are as that trip did, and it really was amazing. Calling them "Bold" is being incredibly polite. They think the (rising) sun shines out of Honda's tailpipe, that they can do no wrong, and that everyone else is lightyears behind them. -- Regards, Noddy. |
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