So.... Toyota Invented Cam Overlap?

[RockJustRock]

i-FORCE is the name given to the Toyota Tundra's powerful V8 engine. This engine uses VVT-i, which stands for “Variable Valve Timing with intelligence” for improved fuel economy. What makes this engine different from traditional engines is that Toyota developed a way to overlap the time between when the exhaust valve closes and when the intake valve opens. This results in drastically improved fuel economy for these larger vehicles that require an 8-cylinder engine.

Who woulda thunk it?

[CTX-SLPR]

I think they are being coy about using an Atkinson Cycle engine which searching for the spelling of showed a ton of Toyota links. Honestly hardly a new thing, GM used it on their hybrid V8 trucks/SUVs years ago.

[RockJustRock]

No.... The reason I find it hilarious is that EVERY modern engine has SOME overlap. Exhaust scavenging in overlap has been around forever. That statement is as if they say "AND we've discovered we can fire the sparkplug before top dead center too". To anybody with knowledge of camshaft science it is like saying Toyota discovered the wheel.

Edit: I Googled Atkinson Cycle. Hard to believe an engine that uses multiple rods and 5-7 bearings per cylinder could work. It says the Internal combustion part of a Prius uses one, still Googling..... With a light load like a charging system it might be possible, but I've been under the impression all hybrids use the combustion to also drive the wheels.

Since the Diesel Cycle is more efficient than the Gasoline cycle because it doesn't throttle air causing vacuum and pumping loss I'd like to see a diesel hybrid. perhaps charging only. Imagine a Tesla with a Diesel generator. Correct me if I'm wrong, but direct injection gasoline still has to throttle air to manage cylinder pressures and power output. A WOT only gasoline generator is a possibility but I haven't seen it.

Edit Part Deux: This article http://news.pickuptrucks.com/2015/01...le.html has Toyota claiming an Atkinson Cycle by using valve timing to bleed compression back into the intake. Note is uses Atkinson in quotes. Even with direct injection the reversion in the intake would be chaotic. One source mentions supercharging, but even a supercharged engine pulls some vacuum at cruise, right Pee Wee?

[RockJustRock]

Since Edits don't bump up posts, another great article: http://auto.howstuffworks.com/atkinson-cycle-engine.htm. Anything that separates performance from efficiency grates on me. We all know the world would be better off with tiny racecar engines powering everything. I'm going back to geeking on motorcycle engine tech.

Edit: AND diesel racing tech!

[Loren]

Sorta interesting article there, once you get past that the author starts out by putting us in the wrong century and she doesn't appear to fully understand what she's writing about. Those kids.... Wikipedia (as usual) has a pretty good explanation including the .gif below of the original thought, and lists some of the mechanical compression ratios used for the modern simulated Atkinson to work, all in the 12-up range. https://en.wikipedia.org/wiki/Atkinson_cycle



By MichaelFrey - Own work, based on US Patent US367496A, http://www.google.com/patents/US367496, CC BY-SA 4.0, https://commons.wikimedia.org/w/inde...curid=41612521

The purple Challenger cruises around town just fine w/ 11.5:1 compression on 91 octane due I imagine to blowing some of the intake charge back out w/ late valve closing, kinda the same thing in that situation.

[Barry Donovan]

cam overlap was used as a retard on draft engines.
builders can use it to be a monster in the end.

the real credit may be the beetle boxer4.
porsche themselves revealed the triple power increase on the same damn engine.
early 60s, late 50s.

given the game of thirds, american is tied in as well.

my 1980s subaru makes bad use of it. I can only go for centered timing, equal chances..cram the overlap.
there is a chance for legend there.. all engines.

[Thumpin455]

Thats an awful lot of complexity to get a half stroke on the intake, lots of angularity, and five separate components reversing direction to give a slight mechanical advantage and limited RPM capability.I can see why you might want to do that in something like a power unit that runs at a particular RPM, but in a car it needs to either turn a generator like trains or have a variable transmission like a hydrostatic drive.

To me its an end around, simply justification to keep using gasoline with its inherent lack of thermal efficiency and crappy octane. Direct injection is the same thing, squirt it in under extreme pressure just before you ignite it in a vain attempt to force the fuel to vaporize.

Cool idea for stationary engines, I bet it would work great with hydrogen or methane if you can get the compression high enough and not have that rocker arm bashing the exhaust valve like that. Yes I am aware a production engine would vary quite a bit, but the principle stays the same. So many things to go very wrong, plus the added weight and deflection issues. Definitely not a 7000 capable engine.

What can I say, I like dead nuts simple.

[Loren]

The end desire for all that monkey-motion is simple, to get the exhaust temp down as close as possible to ambient; the theory being when happens you would have used all the power the heat of combustion could give instead of blowing it out the exhaust...but yeah, the contraption to further that idea is not simple.

Most simple of all is a Wankel, which also has the greatest rpm capability, and is also the least efficient.

[RockJustRock]

The Atkinson has too many bearings. The Rotary has too many seals.

Here's another idea. If the power stroke is so important why not push it into another cylinder running just two strokes, secondary power and final exhaust?

[Loren]

Kinda like turbo-compounding https://en.wikipedia.org/wiki/Turbo-compound_engine except with a piston?

[AndyB]

More like a multi-expansion steam engine.

[Stewzer55]

Exhaust heat could be used to power a supercharger of sorts could it not? Use a turbine in the exhaust to extract the heat energy and use that force to power and impeller to create more power when needed and more efficiency when not. Wait, that's a turbo charger... Turbocharged Direct Injection Otto Cycle is going to be difficult to beat, GM's 2.0T engine makes really good power with little lag in any platform I've experienced it in, lots of torque with the turbo

[RockJustRock]

The inefficiency is the fact we are used to RESERVE power, not just what is needed to get down the road. A turbocharger on Otto cycle just compounds that "problem". That is why I'm bullish on diesel. Gasoline has to be lit JUST RIGHT or it detonates and knocks. Direct inject it too late and your energy goes out the tailpipe. Thus the luxury of extreme compression (and expansion) ratios with diesel fuel and throttling by fuel metering rather than air. To maximize efficiency with Otto cycle you need minimal acceleration capability (who wants THAT?) and roads with no hills.

[cstmwgn]

The inefficiency is the fact we are used to RESERVE power, not just what is needed to get down the road. A turbocharger on Otto cycle just compounds that "problem". That is why I'm bullish on diesel. Gasoline has to be lit JUST RIGHT or it detonates and knocks. Direct inject it too late and your energy goes out the tailpipe. Thus the luxury of extreme compression (and expansion) ratios with diesel fuel and throttling by fuel metering rather than air. To maximize efficiency with Otto cycle you need minimal acceleration capability (who wants THAT?) and roads with no hills.

I am confused - I just want the tires to smoke when I hit the pedal!

[Jimbo17]

I have always found it interesting what you can learn when profiling a cam with a degree wheel and checking value location for every degree of crankshaft rotation.

Cylinder compression is another fun thing to fool around with. Having a late exhaust value closing sure helps pulling in a new fuel charge on most engines.

Ernie Elliott gave an interesting talk years ago on swirling fuel into the cylinder and he showed how much more fuel you can get into an engine before it fires!

Just my opinion. Jimbo