h a l f b a k e r yRenovating the wheel
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"Give me a lever long enough, and a prop strong enough, and I can singlehandedly move the world" - Archimedes
it seems to me, that the biggest problem in creating an efficient car, is stopping it from working too hard. cruising along on the motorway, a car engine is turning over at something around
3,000 rpm, and churning through 100bhp+. all you actually need though, is just enough power to fight friction. if you had a gear high enough, your engine could idle at a few hundred rpm. problem is though, you'd go no quicker if you put your foot down, and nobody wants to drive a car with 17 gears (let alone pay for the gear box).
i drive everywhere with my engine nicely in the powerband, because it's fun - but it's a huge waste of fuel. what i'd want ideally, is to have the car idling when i'm cruising, but ready to sacrifice my efficiency when i'm being over taken by some pillock in a bmw. the way to do this, is with a cvt - controlled by a computer.
when you put your foot on the accelerator in a regular car, what you're doing is letting more air into the engine; what i'm proposing is a drive-by-wire accelerator. the eccelerator pedal is read by a computer, which decides what speed i must want to go, then controls the cvt and the engine to take me there. when i'm accelerating, the computer will keep me in the power band. when i'm happy with me speed, i'll lift my right foot slightly, telling the computer to accelerate no more, which will in-turn tell the engine to slow down to just above tick-over, while controlling the cvt to maintain my actual road speed.
there'll obvously be a slight lag if you suddenly put your foot down, put probably less than actually changing down gear your self. of course, now the transmission and throttle are computer controlled, you could always introduce a 'sports' mode, with maximum power never far away.
onto the 100mpg claim. ignor the current stock of hybrid cars - they're useless. the most efficient car i know of is the diesel vw lupo. it'll do nearly 90mpg on a nice run, but it still tries too hard when cruising. suck up fuel about 15% slower, and you're on a winner
Archimedes Lever
http://www.mcs.drex...ver/LeverIntro.html
In the original language plus various translations. [DrBob, Dec 20 2004]
[link]
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Drive by wire is baked, burnt, and flambe'd. The primary problem becomes one of horsepower sufficiency at speed. Not enough at lower rpm's, sorry. And because of things like CAFE standards, the engines of most cars are geared towards a nice mix of efficiency. Simply slowing the engine down is not going to do the trick. |
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CVT's are still a bit clunky in execution; the belt isn't terribly efficient yet. Using the CVT as a speed-set and engine for variable ramp-up power is a bit more novel, but also probably baked in more complex forms. |
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//"Give me a lever long enough, and a prop strong enough, and I can singlehandedly move the world" - Archimedes// |
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That Archimedes was fantastic. When everyone else was speaking Latin and/or Ancient Greek, he came out with such wonderful quotes in English. Reminds me of an Al Murray put-down to a heckler of Greek extraction: <pub landlord> "The Greeks are a wonderful people. They invented philosophy, astronomy, mathematics, democracy and the scientific method - then decided to put their feet up for four thousand years" </pub landlord> |
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Getting to the idea, will this really give 100mpg? From what I remember reading CVT's tend to be less efficient at transferring power from engine to wheels, and that's one reason they aren't widely used. For info the VW Lupo diesel actually manages something around 80mpg, compared to 66mpg for a Prius (best hybrid). But then Diesel is a more energy dense fuel. |
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Ideally, you could control the power produced by an engine without having to throttle it by using gearing to change the speed. Within certain limits, this would probably be workable. Unfortunately, unlike steam engines which can run equally well at 1RPM and 1,000RPM, gasoline-powered engines have minimum speed requirements. |
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The difficulty is that engines rely upon the fact that by the time most of the gasoline has burned the piston will have moved well past TDC (top dead center). If the piston were not well past TDC by the time all the gas burned, the pressures would be quite excessive; the engine might easily blow a gasket, rod, or whatever else gives first. |
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The situation is made worse by the fact that the higher the pressure the faster gasoline will burn. If the piston isn't moving fast enough to reduce the presure, the gasoline will burn even faster than if it were. |
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Throttles are lousy wasters of energy. A number of alternatives to throttling are being used by various researchers, and some of them seem very promising. Although a CVT might be a useful adjunct to these improvements (being able to keep the engine operating in its peak performance range while going 0 to 60 might allow a smaller engine to provide performance comparable to a larger one) varying engine speed alone is not an adequate means of controlling power. |
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Hang on, no. This isn't right. [seanbo] appears to think that power is for acceleration, and that the only thing slowing you down again is road friction (feel free to correct me if I am mistaken, [seanbo]). Wind resistance consumes the overwhelming majority of a car's power output at speed - drag increases with the square of the car's velocity. Hence, at high speeds, you need most of that 100bhp. |
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david_scothern - when i said friction, i was including that with the air. if you can accelerate, then you must be producing spare power. |
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cvt inefficiency - okay, i know the world hates cvt transmissions, but there have been advances. forget belts, they're too elastic. look at ratcheting cvts, or the anderson cvt |
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lower rpm - cruising at high speed, you're turning the engine too fast to be burning all the fuel. engines do have a minimum working speed, but they're most effient rpm isn't much higher than this. you might not be producing enough power to maintain speed at this low rpm, but you should be able to run a bit slower. |
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I'm not sure about the basic premise here - but please correct me if I'm wrong. Just because your car can produce 100 bhp at 3,000 rpm (and using all the fuel that 100 bhp requires) doesn't mean that it's always producing 100 bhp at 3,000 rpm - it could be producing considerably less and using considerably less fuel. |
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//if you can accelerate, then you must be producing spare power.// |
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No. If you were producing more power than required to overcome friction and drag, there would be a net force and the car would be accelerating. |
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If you're at a steady speed, all the power your engine is producing is being used to overcome friction with the road and aerodynamic drag. Put your foot down to accelerate, and the engine will use more fuel and produce more power, allowing you to accelerate to a higher speed. At this higher speed, friction and drag again balance the power produced by the engine and the car stops accelerating. |
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<aside> When I was about five, I specifically wanted a car with 17 gears </a> |
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I thought belt drives were very efficient. Maybe not in a CVT config? |
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look, i thought i was on to something here, but perhaps not. i maintain that my basic point is sound though. engines do not burn all their fuel at a high rpm, where-as they more or less do when they're turning slower (because the fuel gets more time to combust). if you can get the engine to turn as slow as it possibly can, while still maintaining speed, you'll burn more of the fuel in the cylinder head, and therefore run more efficiently. |
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What controls the amout of fuel burnt in the cylinder is the amount put in. Although very high performance engines do put excess fuel into the engine, normal road cars don't if they are running properly (catalysts get really pissed off if there is any fuel in the exhuast). The system you are proposing would allow the engine to run at its most efficient speed so there would be some saving assuming the transmission didn't eat it all up. |
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seanbo: You would be onto something were it not for the difficulty of controlling combustion rate. In theory, an engine operating running WOT at 600RPM would put out 1/10 the power of an engine running WOT at 6,000RPM. If that were the case, using a transmission like you describe would indeed be an efficient alternative to throttling, so I don't fault you for thinking of the idea. Unfortunately, engines will "lug" when run too slowly. |
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[Gordon Comstock] //Just because your car can produce 100 bhp at 3,000 rpm (and using all the fuel that 100 bhp requires) doesn't mean that it's always producing 100 bhp at 3,000 rpm - it could be producing considerably less and using considerably less fuel.// |
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If the engine is operating at wide open throttle, power is basically a function of speed. If the engine is running throttled, the power output will be reduced, but the fuel consumption will not be reduced nearly as much as power. |
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what's improtant to remember, is that just because you're burning all the fuel, doesn't mean you're burning it efficiently. at high revs, even in an efficient engine, you get more carbon monoxide, and less carbon dioxide. you get less energy when your carbon only finds one oxygen. |
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[Just because your car can produce 100 bhp at 3,000 rpm (and using all the fuel that 100 bhp requires) doesn't mean that it's always producing 100 bhp at 3,000 rpm] |
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Well yes to maintain 3000 rpm the engine should suck in just enoungh air and just enough fuel will be added to maintain a correct fuel air mixture (and rpms). Why then do different cars produce different gas mileage? My car is particularly thirsty 2000 turbo and at 3000 rpm air is being pumped into it... so it seems that some cars are tuned for gas mileage and some are tuned for performance. |
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What might be quite nice is a more variable throttle body or head. I friend of mine recomended restricting my induction system to reduce the amount of air entering the engine. I think porsche has a variable head with three settings reducing or increasing air flow into the engine based on rpms. This will reduce the power output and fuel consumption although the results will not be optimal. |
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Most modern cars are now fitted with ECU's that can be reprogrammed. One popular modification is to load two fuel maps one for economy and one for performance. This modification replaces the stock ECU's single map for all conditions. (I think porsche now has this as well...). |
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Back to the idea... It will work if the car is retuned(reprogrammed) to do the right thing when the throttle is pressed. |
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a FIAT, running of 'Hallucigenics' of some intenal staem power, in the just standard ICE/ERG/???, micro-'phessor'' thing, will not yield less to that 27.00 -29.88 revolution's Per Minute !!, actual experience !!, let go of the clutch, try to brake it on the Pedal, nothing stops it !!,,.. The garage wouldn't know of it, but put it apart, and I picked up another sort of 4 pass. car, (AVIS in Bologna, 2002 yr,.),. |
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I think power at 6.00 to 6.000, might be something like 100.0000.0000 times the value, since actual 'Work' and 'Weight', versus 'The Torque', and Air Flow dependencies, are so much more important !!, rev's again... :-) .. s. |
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That's because your missing the Godel references.
In-joke. |
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