Toyota targets 45% thermal efficiency for engines in next-gen hybrids

"..It doesn't make sense to combine hybrids and turbos.."

But with hybrids using the Atkinson cycle concept it does make sense to use SC.

But the point is that the Prius engine is already too big for its britches...

SuperCharging would allow the engine volume to be reduced to an even greater extend resulting in an engine more well matched to the major time of need, simply cruising along at a relatively constant speed.

"...Electric motors are essentially turbos..."

But the electric motors are simple a means to make use of the FREE "fuel" regained when using regenerative braking. Without a source of that "free" energy the electric motors would represent a NET loss.

Just as they already do in highway/freeway driving.

Which is where the SC would SHINE.

 

The efficiency gain attributable to DI is the result of the ability to increase the CR by ~ 20%

A high(er) compression ratio is really of a benefit ONLY when/if the cylinders are recieving a FULL charge of A/F mixture...at or near WOT. Hybrids are designed for efficiency for cruisng, not WOT.

Plus which the delayed valve closing technique PREVENTS full cylinder filling, pushes ~30% of the initial charge back out into the intake manifold.

 

Do you have a source for it? Would love to read about it.

Can you name one Atkinson cycle ICE with DI? I am not disagreeing with you. It appears the next step to the Full hybrids are DI, probably when the cost is lower. 42.4% thermal efficiency is awesome.

The percentage is meaningless without knowing BSFC across the RPM range. Gen2 and Gen3 ICE has 37% and 38% respectively but the EPA MPG is about 10% difference. It was due to Gen3's ICE having better BSFC across a very wide RPM range.

 

If your primary objective is power, then I agree with you. If your primary objective is fuel efficiency, then it is expansion ratio that matters.

That is the reason the Prius engine uses a psuedo Atkinson cycle. It has a higher effective expansion ratio than effective compression ratio.

Actually, a higher compression ratio improves part throttle thermal efficiency on a conventional Otto cycle engine at part throttle too.

 

First I am not describing DI as a silver bullet. We are not killing vampires here. It is an obvious way to increase efficiency and does cost more. I would expect most engines to make the trade off as auto companies bring the cost down of DI. The article clearly says Toyota is looking to DI to improve efficiency.

I would expect our prius engine also to work well with vvt but electronic valves can extend this range of valve opening and closing to either let in more air or reduce pumping losses. Of course the aggressive egr system has similar benefits so I'm not sure if electronics add much of a benefit.

Ford fussion hybrid and hyundai sonata hybrid. Both companies are aggressively adding DI and turbo charging.

Well, I'm not sure if its a mistake but there does need to be wasted efficiency. If you can wring it all out with other methods then waste pressure will be minimized.

Turbo will only sacrifice cruise mode FE if you don't need the power. So for a given power level a turbo engine can be smaller and lighter, and may allow a more efficient engine in the car. For the prius, I'm not sure if much smaller makes much sense. There seems to be an optimal cylinder size so shrinking the engine may mean going to 3 cylinders and that impacts NVH. Moving from a 6 cylinder normally aspirated engine to a 4 cylinder turbo makes a lot more sense. Future tech like DCCI is compatible with DI but not turbocharging.

The article does say that the toyota type 2 prototype actually has a higher peak efficiency than the engine without turbo charging. I'll leave it to someone else to figure out if that is true at moderate cruse power levels.

 

Does anyone know the peak efficiency of the Chevy Volt ICE?

RPM & Torque would be nice as well.

 

"...Turbo will only sacrifice cruise mode FE if you don't need the power..."

The highest compression available in a normally aspirated production passenger car ~10:1, ~12:1 for DI. Using a turbo alone DOES NOT allow you to increase those factors. Now add intercooling to pre-cool COMPRESS atmosphere and you might get to 15:1. Just think of it as being able to compress the cylinder charge but without raising the charge temperature.

As you can see, the more of the cylinder atmospheric charge that can be compressed and then COOLED before entering the cylinder the higher the effective CR can be.

But you can also go the other direction, most do. Lower the base/native CR to ~8:1 and then "effectively" bring it back up to ~15:1 via the turbo.

But. That means off-boost CR, idle and cruise CR, is abysmal in comparison to a non-turbo engine.

That's basically what's wrong with Ford's EcoBoost, TWINFORCE, DI turbocharged engine design. With DI the CR could be >12:1, but to provide "head room" for turbo boost the engine is left at <10:1.

So cruise FE is sacrficed for STELLAR on-boost HP/torque.

 

Bob Wilson had charts but I can't search for them. Here is one reference
Increasing EGR flow for better mileage - Page 5 - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

I can't find anything athoritative and easy to find. It is quite understandable why Toyota would word on EGR for the prius first. It decreases Nox as well as increases efficiency. DI only adds efficiency.

 

PSD = Power Split device..?

D4 = DI..?

Please explain.

Adoption of DI would allow the engine displacement volume to be reduced while maintaining the same top end HP and thereby improve FE substantually.