h a l f b a k e r y"My only concern is that it wouldn't work, which I see as a problem."
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Ok, I put this in the car section because I figured more gear heads would see it here. I have been recently reading about Ducati's new race bike that is capable of running in 2 pulse or 4 pulse mode. Meaning it can fire 2 cylinders at a time or in sequence 1,2,3,4. But they have to change the configuration
of the bike to do it. So taking their idea one step further, why not develop an inline four that is capable of firing 2 cylinders at a time in the lower revs to improve torque/hp, and move to a inline four configuration as the revs climb, where the inline configuration works better than the twin. I guess you would require some sort of pneumatic or electro mechanical system that would operate the valves of each cylinder independantly. Fuel injection would easily take care of fuel delivery.
(?) Inline Twin Engine
http://members.fort...kymaster/cf-jip.jpg
04 Dec 02 | What I think of when I see the phrase "inline twin engine." [35KB image]. [bristolz, Oct 04 2004]
(?) Valiable Timing For Internal Combustion Engine
http://www.shouldex...002/11/10/204114/51
Would this be similar? [LoriZ, Oct 04 2004]
[link]
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Or why not just split the crank and cam shafts and vary the angle of linkage of the crankshafts? You could actually do the transition smoothly if each pair was capable of running independently. |
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Sounds a lot less Rube Goldberg than the V8/6/4 thing in econobox era Cadillacs. Would this have to be an either/or thing, or would some kind of continuum be workable? |
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unlike the cadillac, this particular idea involves using all four cylinders all the time. You just either fire 1.3 then 2,4 for good strong torque, or 1,2,3,4 sequentially which helps build revs that equates to hp. |
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Which is better: Turbocharging or 2/4 pulse mode? |
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Very interesting idea, and I'd imagine very useful when first gear goes out. |
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[IVnik] Unfortunately inline fours always have two pistons going up as two go down. Otherwise the vibration would be destructive. But I do like the idea of making it switch with the gear selector. But I have a bad habit of riding around town in 5th-6th gear at 3000 rpms and always wish I had more torque down low. |
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[Thumb], as IVnick says turbo lag doesn't suit a bike very well. It even becomes dangerous. If you twist the throttle in an emergancy the bike can have a bad habit of generating 20+hp 2 seconds after you need it. This can be disconcerting to say the least. see link |
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IVnick8or: on this idea, a turbo would probably work very well, since two (or four, using your anno) would produce a lot of exhaust gas at once, meaning quick turbo spool-up. (This anno might work better for car engines than motorcycle ones, using TBK's reason.) |
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Just to clarify, most four bangers, or at least the inline ones, would have 1 and 4 or 2 and 3 up at once not 1 and 3 or 2 and 4. |
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I once saw a motor built out of 2 V.W. boxers, running on one distributor, and the cranckshafts where mated together, always firing 2 cylinders at a time. It seemed to work well for pulling things out of the mud and such, but it was also running through 2 transmissions on a homemade tractor..... |
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Oh well, some people just have too much time on their hands... |
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http://www.usatoday.com/money/autos/2001-05-21-gmidle
.htm |
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I don't see how changing the power pulsing makes much difference, at all, in torque. Everybody knows big V-twins have less torque than the equivelent inline four sportsbike motor. The smoothness of power output helps to ensure as much of the power gets to the road. The 1,3/2,4 would suit high revs more and the 1,2,3,4 would be smoother at low speed. Also exhaust pulse tuning would be different hmmm...
Or am I wrong? Ducati have something up their sleeves? Anyone know?
There are alot of turbo bikes around actually. I've riden a GSX1000 with a low blow turbo. I didn't find it dangerous as the turbo was very progressive and extremely controllable. There was only a 1 second lag at worst at low speed, at high speed of course it was very instant-on. I think the electronic boost controller made all the difference. Then there's wheel stand effect :) |
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I have read that, with off-road bikes, fewer power pulses offer better traction in soil as the tire has more time to gain purchase before the next pulse. I have no idea if this is really the case or not. Sounds plausible, though. |
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Varying the timing would do nothing to switch between the two modes. The positions of the pistons are ultimately determined by how they sit on the crankshaft. In order to do this, you'd have to rotate two of the pistons on the crankshaft 90 degrees. Which is... easier said than done. |
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What rapid_transit said. You couldn't just vary the timing; you'd have to twist that heavy-duty crankshaft to agree with your configurification, or put in a nwe one (far preferable). That's why they had to reconfigurify the bike to change it to a different mode. |
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i would of thought that the two would produce equal power out. double the torque for half the time, or half the torque for double the time.if you could switch from two stroke to four strike were talking. |
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An engine that fires two cylinders at once (4 cyl), does in fact have better traction, because of less pulses. It also makes the same torque and horsepower as one that fires them independently. An engine that fires two cylinders at once, also makes more horsepower with a turbo. Less pulses giving more spool time. It also stands to reason that an engine that fires two cylinders at once will have more engine braking, making it far better for a closed circuit racetrack. This is why V-6's are so fast on a circle track and everybody thinks it's front end weight and chassis balance (this coming from a race car guy). I have never driven a motorcycle. |
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It would be quite easy to do with electronic valves. However, we don't have those in common circulation right now. |
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You'd have to have two sets of cams running to be able to switch on the fly, and a way to lock out each one when the other is running. |
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While a 4-cylinder, 4-stroke engine normally has two cylinders at TDC simultaneously, one of them is on the compression stroke and one is on the exhaust stroke, put another way, one of them has no valves open and the other has an exhaust valve open. |
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On another board I frequent, this was suggested as a permanent situation for inline sixes, which are essentially two I-3's joined together. With a differently-ground cam and a modification to the ignition system, it's a done deal, but you can't switch on the fly. You can only go back by reinstalling the original cam and ignition setup. |
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But you also have balancing issues. An I-6 has the best balancing of all engines. Disrupting that natural balance would probably offset any advantages gained in ganging up the cylinders. |
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But there's another issue: Taking the 4-banger example, you'd be going from one firing every 180 degrees to one firing at 0 degrees, a second at 180, and nothing for another 540. That's not a smooth running engine, regardless of torque. A big flywheel might compensate, but it might also rip off at the shaft in short order. |
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