Featured What did they do to increase the mileage of 2020 Highlander?

6 to 4 cylinder?

 

Yes, and also a increase in efficiency.

 

No idea but I know what happened with the RAV4-h

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Less gas in, the higher the mileage?

 

Going to disagree.

Like any car using just gasoline, the engine is the important part for fuel efficiency. The hybrid system helps, but it helps by allowing the engine to be run at a more efficient point for longer periods. Hypermilers can get near hybrid numbers by doing manually what hybrids do automatically. The hybrid system also allows the engine output to be sized to its most common use without compromising performance during the short periods it is needed.

Look at the gen2 to gen4 Prius. The fuel economy improvements were mostly due to the engine improvements. The gen3 got a larger engine, but changes, like moving accessories from belt to gear driven, meant the range of engine speeds in which it was operating at a higher efficiency was larger than the gen2's 1.5L. The gen4's got a peak efficiency of 40%. That is approaching diesel levels of efficiency.

Better yet, look at the Outlander PHEV. The original engine, which we still get, is an Otto cycle one designed for a non-hybrid. The hybrid system helps, but it can only do so much with a less efficient engine. The new SUV got an Atkinson cycle engine designed to work with the hybrid system, and there is a noteable improvement in efficiency.

Improvements to the hybrid system help, but they help but leveraging the engine's efficiency more. The engine can be kept running at an efficient point for longer periods, or just shut off for longer and higher speeds when it would move into low efficiency operation zones.

The RX and old Highlander hybrids were power hybrids with the V6. The current RX 450h fuel economy is only impressive compared the the RX 350, it isn't among hybrids. The new Highlander's fuel economy jump because of the switch to the 4 cylinder. An engine that lets the non-hybrid Camry beat the past Camry hybrid on the highway.

 

The smaller ICE is only part of the changes. The move to the 4th Gen HV system means a thousand little changes that all add up to MPG.
The Rav4 unproved MPG over the Gen3 HV system by 8-10%, and this was with the same (somewhat redesigned) ICE .I drove them both.
The Gen4 system has much improved battery and charge/regen power management. Lets credit the inverter/converter for that. The 4-cyl ICE is generating more or less the same power to haul the Highlander around as the 6-cyl does, and while its a more efficient engine the difference in MPG is probably less than some folks think. Point being that the Rav4 saw the same jump in MPG without a change in ICE.

 

Well this Rav4h owner can live with an extra 30 seconds to fill my tank at the slow setting. Made more pleasant at $1.939/gal today. There are others who complain on every thread in the forums, whine mightily and demand a perfect car. I look at mine (7.2k miles) and ask what I could have bought that would be more trouble free. No reason to visit the dealer other than to get the tire pressure reset from the 50 PSI they ship with (to reduce wobble) and to get an oil change just because I'm old school and like to have a change at between 1 and 2k. Not a rattle. Nothing I use doesn't work as documented. I can wait till a fix is available and if it isn't, I can still happily live with it.

 

It was a major change between the engines of the Rav4 hybrid.

The old one was port injected with 12.5:1 expansion ration. The new one is 14.0:1 using a hybrid port and direct injection system. In addition to making the engine more efficient, it can produce more power; 26hp more than the old. The combined system power is 194hp to 219hp. The new model manages that with less powerful motors.

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Reports here are that the new 2.4 litre Outlander engine "... can switch from the more efficient Atkinson cycle at low revs and loads to the more conventional and punchier Otto cycle when more is demanded of it." Not sure how that happens - I tried to find out, but can't see anything.

 

I don't know for sure what Toyota did, but on a theoretical level this could be accomplished with an intake cam cut with a blended profile and a wide-range variable phase adjuster. Really, just an extension of variable valve timing as it presently exists. Phase it earlier for higher compression and more power, phase it later for increased expansion efficiency.

 

Found this in WIKI (Atkinson cycle article):

"A modern variation of this approach is used in some modern automobile engines. While originally seen exclusively in hybrid electric applications such as the earlier-generation Toyota Prius, later hybrids and some non-hybrid vehicles now feature engines with variable valve timing, which can run in the Atkinson cycle as a part-time operating regimen, giving good economy while running in Atkinson cycle, and conventional power density when running as a conventional, Otto cycle engine."

 

Do take in account that the Otto compression limit (knock trouble) is a bit lower than the Atkinson practical limit...

 

I think the ICE version of Toyota's new engines can do this. It is basically wide range variable valve timing. Hybrids don't really need the power boost, so they save some cost not using it there.

Direct injection allows higher compression in Otto with lower octane.

 

https://www.motorreviewer.com/engine.php?engine_id=127

The 2.5L engine has CR of 13.0:1 Otto and 14:1 Atkinson.

 

The port injected predecessor has a CR of 10.4:1 for the Otto and 12.5:1 for the Atkinson. The higher ratio, and closeness to each other, in the new engine is because of the direct injection.
https://www.motorreviewer.com/engine.php?engine_id=77

13:1 is probably the limit of compression for DI Otto on US low octane regular. It is what Mazda's SkyActiv-G is at for here. For the rest of the world, it is 14:1. Since it is direct and port injected, Toyota's engine may not be able to go so high, or maybe it can.

When discussing the Atkinson cycle, compression ratio is poor term. The value is really its expansion ratio. The effective compression ration of the charge stroke is always lower for these engine. Close to what a naturally aspirated Otto engine has for the fuel. Toyota could have left the CR at 13:1 for hybrids, the thermal efficiency is at 40%. Instead, they chose to trade some power for efficiency by stretching the expansion ratio a little bit. It is possible the Atkinson version has a narrower range of valve adjustment, if this would mean lower costs.

PS: came across a site referring to the Atkinson as a Miller cycle. Technically they are right, in that the mechanics of today's Atkinson engines are the same as a Miller, and nowhere near how an actual Atkinson engine worked. Miller's design had a charger(turbo or super) though, so Atkinsons of today is only part Miller in execution.