So I read a few background articles about CVVT and I think they are approaching the "Atkinson-style" operation using alternative mechanicals. The holy grail is having a very high expansion ratio without exceeding the BMEP limits at ignition. So the slight increase in fuel efficiency I can see. A slightly-lower amount of friction is probably from switching to 0W-20 and a few other changes. An increase in HP? I don't see how.

 

Well, right there is probably one of the answers. Simply cutting down on the internal engine friction with the thinner oil, especially if it is synthetic oil which will not break down at higher temperatures, will allow more of the engine's power to reach its output shaft.

 

I found the following descriptions of CVVD and the new engine that will use it. [[url=https://www.greencarcongress.com/2019/07/201090703-cvvd.html]Source]

On the surface, this new engine seems similar to the turbocharged on-demand Atkinson cycle engine used in the Lexus NX 300.

This seems to be very similar to Toyota's on-demand Atkinson cycle engines that switch between the Atkinson cycle at low load and the normal Otto cycle at higher loads (using Toyota's VVT-iW valve control technology).

Atkinson cycle engines are very efficient but generate lower torque than Otto cycle engines.

So, this is a turbocharged gasoline engine using the current technologies, including turbocharging, exhaust gas recirculation (EGR) and advanced thermal management. Turbocharging increases torque and power, while EGR lowers emissions; the thermal management system helps lower emissions and increases efficiency.

 

No it’s not similar. Hyundai’s invention can variably change the DURATION the valves are open, not just the opening height and offset of the open/close cycle at different points. Normally the valve close is a fixed time after the valve open, driven by the camshaft alone i believe. Some tricks have been done in the past with moving the camshaft for different lobes to engage i think, but this CVVD is more flexible.

Good explanation here.

https://www.piston.my/2019/07/03/vvt...-group-wvideo/

 

It’s also not triggered at specific rpms like vtec/vvti, but can adapt at all engine speeds and other conditions.

https://www.autoindustriya.com/auto-...ve-timing.html

 

Disclaimer, i have no idea how much of a difference this makes or if it’s reliable, etc.

since i expect my next vehicle will be electric, i also don’t really care.

 

CVVD cannot be compared to Toyota's VVT-i nor Honda's VTEC, which are simpler, earlier-generation valve control systems, but it looks similar to Toyota's VVT-iW (Wide), which is used in Toyota's on-demand Atkinson cycle engines, which runs on the economical Atkinson cycle at low load and switches to the normal Otto cycle at higher loads.

At low loads, VVT-iW implements the Atkinson cycle by delaying the closing of the intake valve past bottom dead centre, pushing some of the intake charge back into the intake manifold; this effectively lowers the compression ratio while raising the expansion ratio (power stroke). This is what is accomplished by CVVD, although I would not be surprised that CVVD is more flexible than VVTi-W.

Your next vehicle may be an EV, but as you know, many people are (still) sceptical about batteries and EVs and will have to be forced, kicking and screaming, into buying one, even within the next 20 or 30 years.

While I am not sceptical about EVs, I am still worried about range and quick-charging, and can see both an EV and a Hybrid (range-extended EV) in our family's future. The EV would be driven by my wife for her short commute and errands, while the Hybrid would be the car for longer-distance driving.

CVVD is just a further evolution of the gasoline-powered internal combustion engine, perhaps the last evolutionary step before the freevalve, camless valve control.

It is proof that there is still life left in the old reciprocating piston internal combustion engine, either on its own or backed up by electric motor(s) in a Hybrid.