Lexus GS Hybrid receives better EPA mpg than Lexus's own tests

So, what's the difference between Toyota's current Atkinson cycle "simulation", pushing ~30% of the cylinder charge back out into the intake manifold, and not letting it get in there to begin with..?

Plus, you get to use the EXACT same engine in the GS and the GSh.

Detune the ICE but raise the electrics capability and end up with roughly the same HP, 338 vs 340.

Since about 2000 the use of low(er) octane fuel in a high compression engine, within reason, has been a non-issue. If even the slightest level of knock/ping is sensed the A/F mixture will be enriched via EFI.

 

Different compression of the engine, which is likely implemented with different pistons. The valve timing is also different to allow the what you call the "simulation". This will give different hp/torque/efficiency in the various implementations of the engine.

Its the same block and dual fuel injection, but other parts are different as is the control algorithm and fuel.

The valve timing is changed, but I would not call the engine detuned. It does have lower hp, higher expansion ratio, and more efficiency. It is tuned for efficiency instead of hp. The hsd also greatly increases efficiency in city driving and allows a more efficient engine to give greater acceleration.

Toyota's vvt is quite different than mazda and fiats electrically controlled input values which could switch electonically. The way the DI is implemented and the combustion chamber design in skyactiv allows for higher compression, but their are efficiency and power gains in toyota's implementation of di+port injection versus their port injection in the same engine block. I coment since you seem to think that toyotas implementation of di, is superior to everyone else's but do not understand why compression is lower.

Designing an engine for higher octane gasoline will reduce its efficiency and power with regular gasoline. You are correct that it won't knock and ping, but why not design the engine for the way it will be used.

 

"..the way it will be used.."

I took factory delivery of a C4 911/996 in '01 and was told that I would not always be able to buy premium in our travels but using regular would not harm anything and I was told why that was/is.

 

The current Toyota HSD Atkinson cycle engine simulation, as in teh Prius, RXh and HH, uses a base/native CR of 13:1 but an effective CR of ~10:1. Note that 10:1 ratio has been pretty much the standard for passenger car high end compression ratio for a goodly number of years now.

With the adoption of DFI that number has now risen to 11.8:1 and above.

If we were to assume the new GS450h used the same Atkinson cycle simulation technique, delayed closing of intake valve, then logic dictates a base/native CR of about 15:1 or more.

Instead the 2013 GSh reportedly has the CR increased from 10.5:1 to 13:1(***). Note that this 13:1 ratio is well within the range of an engine adapted to DFI alone, excluding any Atkinson cycle simulation.

That 10.5:1 number that was reported gives me to suspect a typo of some sort. The current GS350 engine, DFI engine, has a CR of 11.8:1.

Then there is the reported matter of "2" electric motors, one for each rear wheel. The e/CVT/PSD uses 2 electric motors internally, do we now have 2 more..?

Or was the reporter outside his zone of comfort?

 

2013 Lexus GS 450h First Drive

Upon reading the above I'm now willing to take bets that the 2013 GS450h is using the same V6 as the RXh and Hh. DFI is a tad redundent with/for an Atkinson cycle engine since the very idea is to NEVER "push" the CR, compression stroke, to the "limit"

 

http://www.lexus.com/GS-2013/hybrid/pdf/GS450h_pressrelease.pdf

After reading the above, direct Lexus press release, I more confused than ever.

Within the PR there is a statement of 13:1 CR, does that actually mean "effective" CR...??

If the base/native CR is ~15-16:1, as it well should be with DFI, that would also explain the bump in HP (and FUEL EFFICIENCY) vs the RXh's non-DFI V6. The 13:1 is quoted relative to the GS350 DFI V6's 11.8:1.

 

The compression ratio is a physical constant, the ratio of the volume of the cylinder and combustion chamber of a piston at the bottom of its stroke, to the volume of the combustion chamber with the piston at the top of its stroke.

The DI+port injection version of the engine provides more accurate measurement of fuel and better mixing of fuel air. This provides both more fuel efficiency and power even at the same compression ratio, the RX is at 12.5:1. It sounds like the GS hybrid still runs on premium gas.

 

Somewhere I have read that SFI is only used during engine idle. That would make sense to me as a way to combat the problem of EGR residue deposits on the backside of the intake valve.

On the other hand DFI is only needed/required for high cylinder charge fills, WOT or nearby. It is my understanding that the primary advantage of DFI is the evaporative cooling effect of the compressed atmosphere.

It's that cooling effect that is allowing the CR to be increased from ~10:1 to 12-13:1.

Premium gas, or not, is no longer an issue for passenger car high compression engines, hasn't been for over a decade now.

 

There are more numbers than compression, and the primary trade off of DI is higher cost versus more efficiency and power. In the GS hybrid the choice is a no brainer.

One reason for greater thermal efficiency of DI cooling and expanding the fuel in the cylinder. Its not the only advantage. In the case of the GS the biggest advantage will be in ultra lean burn mode where the charge is concentrated by the spark plug. EGR will further reduce polution in this mode by keeping the engine cooler. Ultra lean burn allows the engine to stay efficient at lower power levels. DI also provides more precise metering in Stoichiometric mixtures, and provides better fuel/air mixing.

Not everything is about CR, please learn that some engines with high CR are inefficient and some with lower CR are more efficient. All things being equal running stoichiometric mix DI will increase CR, efficiency, and power.

Again they will not ping but other things do matter on premium. I do not know if this lexus engine does though, since it seems a later valve closing could make up for the difference. Premium might allow for a more lean ultra lean burn also. Before I had a GS, I had a turbocharged car. The owners manual said that it was ok to use regular in an emergency, but regular use would cause hotter exhaust that might hurt the turbo. I'm sure you didn't even notice the slight loss of power and efficiency on your 911. I think mazda said on the skyactiv 14:1 compression hp would be reduced 5% and efficiency 3% using regular, that is why they have a lower compression version for regular gasoline.

 

The advantages of DI come into play only when the compression heating due to the high(er) compression would otherwise threaten detonation.