Car Tech 101: The Atkinson Cycle engine explained (On Cars)

The Atkinson Cycle engine may be under your car's hood and you'd never know. Brian Cooley discusses the technology and why it's becoming a mainstay in late model, efficient cars.

[Guy_de_Loimbard]

The big drawback of the Atkinson engine isn't necessarily the lower overall horsepower number, but the major lack of low-end torque. The existence of an electric motor, what with all its torque available at zero RPM, overcomes this deficit and makes an Atkinson motor practical nonetheless in a hybrid despite its erstwhile shortcomings. Yes the electric motor helps at higher horsepower/RPMs too, but not nearly as much as it assists with initial oomph.

[Iflyagrasshopper]

Atkinson's most successful design was a 2 stroke called the Utilite' . He made that version in 1893. it had the same feature of a short compression stroke and a longer expansion stroke but it used a conventional rod and crank.

[dj]

We know it works well. Prius's have been known to go 300k using the same battery and engine. I think Rav4 hybrids use it too, but as it says, the electric motors make up the difference to give it about 15 hp more than it's gas counterpart.

[dannybryant]

Essentially you have an Otto cycle engine set up for a crazy high compression ratio (to get the crazy high expansion ratio). But u don't want to have to buy high octane aviation gasoline so u need to defeat some of the compression ratio. To avoid crazy high pressures the intake valve is left open longer to exhale some of the air/fuel back into the intake manifold. It's the high expansion ratio that makes the durn thing so efficient.

I wonder if at higher elevation the computer instructs the intake valves to revert back toward Otto to keep more of the (thinner) air/fuel in the cylinder? Like free turbocharging for high altitudes.

[rangersmustang]

Its the "wonky linkages" that make an Atkinson engine what it is. The linkages allow for the complete cycle to be completed in 1 crankshaft revolution. That's what makes an Atkinson engine unique.

[DailyRealness]

1:35 Wonky? It looks genius. People were expert engineers back then. Their math skills were way above.

[drewkwful]

This is also known as a Miller Cycle by Mazda. Essentially the difference is Miller Cycle engines are supercharged and leaving the intake valve open longer gives more time to charge extra air and fuel into the cyclinder.

[RonanTetsu]

In a kia niro, you know when the electric motor helps. It makes shifts feel very smooth (kia hybrids use a dual clutch transmission), though in "sport mode" it's very jolty but wayyyy faster

[Funkbass]

An Atkinson cycle requires that the piston connecting rod be a double pivot linkage. Because of this, it’s essentially a one stroke motor, completing the 4 stroke process in one crankshaft revolution. This being showcased here is an Otto cycle with variable valve timing, something the Atkinson cycle did not have.

[BigRodd]

Sooo you're saying the Atkinson is the low flow toilet of engine cycles?!

[zking]

A lot of Toyota non hybrids are using it now. The 2016 Tacoma was the first and it was a V6

[Nhatnamshare]

longer burn stroke, shorter compression stroke to save the power. That's all i understand about Atkinson cicle.

[philips]

So what happens to the fuel that gets pushed out through the intake valve?

[TexasHarleyBoy]

Hey Nissan is fine tuning that 'wonky linkages thing' with their variable compression 1.5t engine. This ought to be entertaining.

[justlolatthisworld]

If it's more efficient i.e. produces more power per unit of fuel, but just produces less power per volume of cylinder, why not just use a bigger cylinder?

[YZRandomE]

So would an Atkinson cycle engine with direct injection lead to heavy carbon buildup since some of the air/fuel mixture would kind of be pushed back into the intake manifold and there is nothing to clean off the back of the valves?

[dannyatkinson]

I can see this system becoming very complex very quickly

[zking]

No one talks about the near ambient pressure at BDC on combustion Sad

[walnut]

Why push air back out, why not just let less in to start with?

[motoresesistemasautomatos.]

Olá, se usar esse ciclo de Atkinson no motor Stirling daria certo? Obrigado