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Scientists Claim Major Leap in Engine Design
An anonymous reader writes "Purdue researchers say they have made a major advance in the design of the internal combustion engine, one that could seriously boost fuel efficiency and cut emissions. A key portion involves building intake and exhaust valves that are no longer driven by mechanisms connected to the pistons, a departure from the way car engines have worked since they were commercialized more than a century ago. 'The concept, known as variable valve actuation, would enable significant improvements in conventional gasoline and diesel engines used in cars and trucks and for applications such as generators, he said. The technique also enables the introduction of an advanced method called homogeneous charge compression ignition, or HCCI, which would allow the United States to drastically reduce its dependence on foreign oil and the production of harmful exhaust emissions. The homogeneous charge compression ignition technique would make it possible to improve the efficiency of gasoline engines by 15 percent to 20 percent, making them as efficient as diesel engines while nearly eliminating smog-generating nitrogen oxides, Shaver said.'"
Nothing spectacular about changing the timing on the valves depending on how the engine's being driven:
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http://en.wikipedia.org/wiki/Variable_valve_timin
According to Wikipedia, VVT has existed since the 1960's. The only improvement I can see (and that's from reading between the lines) is that they've developed a means of controlling it more precisely.
It's not just Purdue working on this, nor is it cutting edge. The idea of variable valve actuation has been around for a while as well as HCCI, which has some problems that are yet to be overcome. One of the notable ones that I recall is simple power. As the Wikipedia article notes, in a gasoline engine, you increase the fule/air charge to increase power. In a diesel engine, you just inject more fuel. In an HCCI engine, it's tough because "many of the viable control strategies for HCCI require thermal preheating of the charge which reduces the density and hence the mass of the air/fuel charge in the combustion chamber, reducing power. These factors makes increasing the power in HCCI inherently challenging."
For more info, the Wikipedia page has some great references:
- Research, publications at Lund University
- Research at Chalmers University of Technology
- Research at Stanford University
- Research, publications at University of Wisconsin, Madison
- Research at University of California, Berkeley
So, it's got a lot of benefits but a few trade offs that need to be addressed first. Honestly, why would Ford/GM buy this out and kill it when they could just develop the technology themselves and integrate it into their vehicles like Hitachi's research? I mean, just because technology changes doesn't mean they should kill it instead of changing with it, right?My work here is dung.
Why keep a cam if you're electronically controlling the valves? Just like ignition systems have gone to fully solid state, with very few cars having distributors any more, why not move to fully digital timing?
The cam/valves are really the last mechanical part of the loop. The fuel/air mixtures are now fully controlled by the ECU, and can change on the fly to adjust for altitude, temperature, manifold pressure (turbo and supercharged systems), and the octane of the fuel. As I mentioned above, the spark systems are now fully controlled by a computer, and advance or retard the cylinder ignition, sometimes in conjunction with the fuel curve, to best burn the fuel/air mixture. Being able to dynamically change the valve timing, opening, closing, overlap, duration opens up even more possibilities for tuning and timing an engine.
I don't know if you've ever had to compress a valve spring, but they're pretty pissed off devices.
The best thing we could do would be to move to some kind of rotary valve system - any kind, really. Because reciprocating valves have problems. They are what limits RPMs, which is why rotary engines have been known to reach over 10,000 RPM, and why a [very very built] small block tchevy :) with a Coates rotary valve system has reached over 12,000 RPM (can't find cite for that, but their page says "The comparative efficiencies of the spherical rotary valve combustion engine have enabled engine speeds of 14,850 RPMs."
We could make smaller, even more efficient engines by increasing RPM, but we don't do that because it causes valvetrain death. In order to get high RPMs, you need to be able to open and close the valves faster. Cams only open valves; springs shut them. This has two effects; one, there is a hammering process that goes on between the valve and the seat. Two, if the springs are not strong enough, they do not push the valve closed fast enough, and you get a phenomenon called "valve float". Solenoids can provide infinitely variable valve timing and duration, and through a shifting system (where the whole actuation system moves) you can provide variable lift. But as you increase RPMs, you need to increase the spring rate, and therefore you need stronger and stronger solenoids.
A solenoid valvetrain has been used in racing (I forget by who) but no one has managed to make a system suitable for the street yet. That's really too bad, because you could eliminate most of the valvetrain that way. But there are definitely serious implementation issues. Rotary valves are here now. There are competing designs, but none with pictures as pretty.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
This is not news. BMW has been playing with this for years. So has Mercedes -- they call it EVT, for Electronic Valve Train. And next year it will ship in the 2008 C-Class sedan.
FATMOUSE + YOU = FATMOUSE
The trouble with direct valve actuation is making an actuator that's fast enough, powerful enough, small enough, heat-tolerant enough, and reliable enough to do the job. Cheaply. This is not easy. Prototypes have been built, but it's still not something that's easy to do. BMW did quite a bit of work in this direction, but backed off to their "Valvetronic" scheme, which still has a camshaft with other components to give some adjustment potential.
Most of the existing schemes for tweaking valve timing still involve camshafts, but there's an additional mechanical linkage which allows adjustment of phase angle, valve travel, or both. That's an idea which goes back to steam engine design. Most of the gear on the side of a steam locomotive is there to adjust valve timing. Steam engines are controlled by valve duty cycle, not throttling. This was the original pulse-width-modulation system. On steam engines, valve phase can be adjusted far enough to reverse the engine, which is how locomotives back up. Some newer marine diesels have that feature, too. Eliminates the need for a reverse gear.
So this isn't a new idea. It's an old idea that's hard to make work cost-effectively. Somebody may crack this thing; it's a tough mechanical engineering problem, but not an impossible one.
Well, no actually. A rotary such as the current Mazda 1.3 litre simply spins faster than the equivalent piston engine. The volume passed per unit of time is the relevant comparison, not the static displacement.
Since the RX8 competes with similar HP sports cars by guzzling at SUV rates, it indicates Mazda's best effort so far is still inferior in power conversion of the gasoline. (Though the smoothness is great fun.)
As for turbines, same deal really. The aircraft turbine has yet to match piston engines on efficiency for short flights. You have to run long-haul at cruise altitude before the overall fuel consumption is lower.
The idea of a completely spinning engine is very seductive, but the actual results of forty years of careful research has not delivered a spinning engine that's better than the 'tossing potatos'. This is counter intuitive, and it's entire worth your while to dig into the studies to find out why that is.
As a Canadian, who has driven in extreme weather for 17 years - ANY car, with proper snow tires, is adequate for almost any situtation you will encompass. The only weather it won't help you with is sheet ice, or huge drifts, and there, you're finished in anything short of a lumber skidder or perhaps a tank.
I easily outmaneuver SUVs on "all season especially winter" tires in my little FWD car with maybe 5" of clearance tops. Because I have enough sense to put proper snow tires on in the fall.
4WD does nothing to help you stop, either.
..don't panic