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Old 03-05-2020, 11:26 AM   #1 (permalink)
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Hyundai CVVD

https://www.caranddriver.com/news/a2...ogy-explained/

Best implementation I've seen, as the mechanical efficiency should be high, and there's no added reciprocating mass which eats power and limits durability at high speed. Very clever!

Typical load is like 50% on an engine, so a 270 degree grind on the intake cam would give minimized sliding friction in the mechanism. At high load low rpm, the duration can be shortened to 210 ish, and at idle it can be increased to 300+ for zero throttling losses.

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Old 03-05-2020, 10:55 PM   #2 (permalink)
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I watched half of the engineer explained video on this the other day. I agree, its very interesting!

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Old 03-05-2020, 11:27 PM   #3 (permalink)
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I know this is pretty irrelevant to fuel economy and ecomodding, but what personally gets me excited about this is the fact that it would work really really well at motorcycle engine speeds.

The Honda F20C had VTEC and 9000rpm, but no other manufacturer has dared to use a heavy switchable rocker or bucket at that speed. Porsche 911 GT3s and the Lexus LFA use fixed cam profiles, Ferrari has their continuously variable profile (which probably has issues with uneven lobe wear) that moves the camshaft around. Some BMW bikes have 2 cam profiles and switch by sliding between them as well, but that system needs I think 1 actuator per 2 cylinders to slide the camshafts while they're not in use, which is annoying.

This is much simpler. No cams moving around, ability to bleed off almost all the VE while also having great low end torque, no reciprocating mass to add stress to the valves, and little friction.

On a motorcycle, you could throw away the ITBs for this, and eliminate all the emissions and fuel economy problems. High revving car engines become much more practical, since you get great torque everywhere, and can use less valve spring pressure.
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Old 03-06-2020, 10:20 AM   #4 (permalink)
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I'm wondering if this will increase the fuel efficiency of their hybrids or just increase the power, and increase the fuel economy on their standard models. Kind of a dual-mode engine.
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Old 03-06-2020, 03:47 PM   #5 (permalink)
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Most likely it may serve for both non-hybrids and hybrids. On a sidenote, if it could also improve cold-start ability with ethanol and allow higher static compression while still retaining port-injection as Freevalve claims its system can do, I'm sure most of the traditional automakers would prefer to follow the Hyundai's approach.
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Old 03-07-2020, 12:15 AM   #6 (permalink)
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I feel like it's kind of not worth it on a hybrid, because on a hybrid car you can just shut off the engine at low load, and use heavy EGR dilution for medium load. Cooled EGR is still good for efficiency.

Then again, Honda puts VTEC on every engine despite the added expense.

I'm not sure if it can improve cold starts, I can't really think of a reason why it would. I suppose you might have some fuel air mix floating around the intake tract that's kind of getting constantly pumped back and forth across the valve, giving it more time to mix with the air, or maybe it just means more fuel sticks to the walls and actually makes things worse.

I think Koenigsegg is full of crap when he says you can use port injection, direct injection is basically always better...

It is useful on a turbo engine for response and efficiency reasons: Say the engine is knock limited at full VE and 1 bar boost. You can immediately go max VE while the turbo is spooling, then as the turbo pressure builds past 1 bar, increase duration to limit torque instead of using the wastegate, and you have a much more efficient engine. This lets you use a higher CR with an intercooler, since the intercooler is rejecting more heat. Porsche does this with a low VE intake on their GT2, basically letting the turbo do more of the work.

The other type of engine it's useful for is the one I described, a high revving NA engine. No more valvetrain problems or low end torque to worry about, only getting the bottom end to hold together at whatever speed you choose.

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Old 03-09-2020, 10:53 AM   #7 (permalink)
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Quote:
Originally Posted by serialk11r View Post
I think Koenigsegg is full of crap when he says you can use port injection, direct injection is basically always better...
Direct injection has the downside of increasing particulate matter emissions on gasoline and flexfuel engines. No wonder Toyota still resorts to the port-injected 2ZR-FXE engine in the Corolla hybrid even though the M20A-FXS featuring dual injection is available for the hatchback and station-wagon bodystyles in Europe.
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Old 03-10-2020, 12:42 PM   #8 (permalink)
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That's true, with stricter emissions standards port injection might be desirable to eliminate the particulate filter. Performance-wise, DI is generally better.
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Old 03-11-2020, 07:35 PM   #9 (permalink)
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Another aspect worth to remind is that port-injection may also decrease the load over the cooling system, not only due to the colder air intake charges but also due to the usually lower compression ratio. Just look at what Ford did with the so-called Godzilla engine.

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