3.5-liter Atkinson cycle V-6

Someone explain the "Atkinson". What/Who is Atkinson?

 

http://news.pickuptrucks.com/2015/01/how-it-works-2016-toyota-tacomas-atkinson-cycle.html

 

And James


James Atkinson

 

Note the engine is rumored to also have VVT-iW or -iE so it probably switches between Otto and Atkinson as required.

 

http://lmgtfy.com/?q=atkinson+cycle

 

Very basic - it has a shorter compression cycle than the power cycle - which improves efficiency.

The original Atkinson engine achieved this through bell cranks and levers. In the modern engine this is achieved by varying the intake valve event.

Intake valve stays open as the piston is coming up, pushing some of the charge back up the intake port. Then the valve closes and you get ignition shortly after.

 

In the animations it looks like gas is being wasted out of the valves. Guess I am not understanding right.

 

Its not wasted.
Its stored.

For the next cycle that charge is ready and only little more needed. Thats where the efficiency comes from.
Remember, as long as the valve is open, much less energy is used moving the piston...

 

Sort of. Not exactly "wasted" just pushed back out to be used in the next stroke.

The basic idea of the Atkinson cycle is to limit amount of gas and air being detonated so that the resulting cylinder pressure at dead bottom of the expansion stroke is equal to or as close to 1 atm as possible (Ie, use as much of the potential energy of the detonation as possible). In the Otto cycle, at dead bottom of the expansion stroke, the cylinder pressure is still much greater than 1 atm and still wants to "do work" but is wasted out when the exhaust valves open.

Otto cycle will make better power as more gas is detonated per stroke but the Atkinson cycle will utilize each detonation more efficiently.

Not really. The efficiency comes from using roughly the entire potential energy of the detonation in the down stroke.

 

You certainly explained it better.

What Im curious about is how the Atkinson cycle reacts with boost?

It will essentially take away from the entire principle of the A cycle.

D

 

Good point, never really thought about that. I don't think Toyota's method would work too well with boost. Would def be harder to push that air back out against the pressure. Probably why Toyota did away with the S/C program?

 

Im thinking maybe a centrifugal might work.
Less boost when down low and anyway, when the throttle plate is closed, it wouldnt go against boost necessarily.
Once boost builds, switch to general Otto cycle?

Could work? Maybe?

 

A boosted atkinson cycle is called the miller cycle. https://en.wikipedia.org/wiki/Miller_cycle.

 

Ah the Miller Cycle. The most successful commercial application for this type of engine was the Mazda Millenia S. Never owned one but they seemed like pretty decent cars.

 

Guys the new Turbo 4 of Toyota/Lexus are Atkinson capable (cycle hybrids). So there is nothing wrong with adding boost to this engines.
They are just playing safe.

 

I think in the Future they may boost this engine and offer it in the Tundra as a EcoBoost challenger. Everyone knows Toyota needs to do something about the powertrain in the Tundra.

 

The shuffling of reliable engines and technology is Typical of Toyota. The performance of the 4.0 is generally lauded and appreciated by the Taco crowd. They just want something more efficient. This seems to be the least expensive way toward that end. This may be the only place the motor appears until it us upgraded more for other vehicles. I din't see The Tacoma being a trendsetter for motors for very long. When we get all the specs, we may see it's mostly made from parts out of the bins of other vehicles an Tundra and Highlander are two good places to start.

 

Who wouldve thought a full size F150 was gonna have a smaller engine than the Taco?

 

That or they will be offering TRD turbo kits like the supercharger kits

 

That should be interesting...

We know the Ecoboost 3.5 is esily capable of 650hp, so who knows??