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#4525486 - 09/25/17 07:47 AM Atkinson Cycle engines on non-hybrid vehicles
JustN89 Offline


Registered: 06/27/17
Posts: 477
Loc: DFW
Just wanted opinions on this question I've been having about the Atkinson Cycle engine. While I know a bit about it and it's definitely not new technology, I had never really heard of it used very often until manufacturers started putting it in their hybrids. It seemed like a perfect fit, an engine that suffers from a lack of low end power and a battery to help make up for that. Now, however, I'm seeing it put into a couple of other applications, including non-hybrid vehicles. For example, the Elantra in my sig has an Atkinson Cycle engine, as well as 2016+ Tacomas.

What I'm wondering is if there's any reason to think that these engines may not experience the same longevity as the standard, Otto cycle engine? Having never seen an Atkinson Cycle engine outside of a hybrid, I really have no idea what to expect here. I mean, there are plenty of 200k+ mile Prius engines out there which are Atkinson Cycle, but the life of a hybrid engine is a pretty easy one.

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#4525491 - 09/25/17 07:53 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: JustN89]
VetteElite Offline


Registered: 04/20/13
Posts: 116
Loc: -
If I'm remembering correctly, non-hybrid Atkinson engines use their VVT systems to simulate Atkinson cycle and can switch to the more powerful Otto cycle on demand.

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#4525503 - 09/25/17 08:04 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: JustN89]
JustN89 Offline


Registered: 06/27/17
Posts: 477
Loc: DFW
That's an interesting point Vette. I hadn't heard that, but that would make sense.

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#4525509 - 09/25/17 08:12 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: VetteElite]
glock19 Offline


Registered: 03/12/13
Posts: 764
Loc: Virginia
Originally Posted By: VetteElite
If I'm remembering correctly, non-hybrid Atkinson engines use their VVT systems to simulate Atkinson cycle and can switch to the more powerful Otto cycle on demand.


I'm not sure about the Elantra, but I know this is the case with the Tacoma.
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#4525511 - 09/25/17 08:13 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: VetteElite]
LotI Offline


Registered: 01/01/13
Posts: 1268
Loc: America's Dairyland
Originally Posted By: VetteElite
If I'm remembering correctly, non-hybrid Atkinson engines use their VVT systems to simulate Atkinson cycle and can switch to the more powerful Otto cycle on demand.

Yup, SkyActiv from Mazda can adjust intake and exhaust valves to achieve Otto or Atkinson. Miller cycle engines, aka Mazda Millennia, add supercharging to make up for the lack of low end breathing.
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#4525516 - 09/25/17 08:19 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: LotI]
4WD Online   confused


Registered: 09/21/10
Posts: 6428
Loc: Texas
Did anyone forget to add "almost" - that's how lawsuits start.

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#4525522 - 09/25/17 08:24 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: glock19]
JustN89 Offline


Registered: 06/27/17
Posts: 477
Loc: DFW
Originally Posted By: glock19
Originally Posted By: VetteElite
If I'm remembering correctly, non-hybrid Atkinson engines use their VVT systems to simulate Atkinson cycle and can switch to the more powerful Otto cycle on demand.


I'm not sure about the Elantra, but I know this is the case with the Tacoma.

Here's what I've found on the Elantra:

"For 2017, the new Elantra receives two all-new powertrains designed for improved fuel efficiency and everyday drivability performance. The standard engine available on the base SE and Limited trim is a 2.0-liter Nu MPI Atkinson four-cylinder engine producing a peak 147 horsepower at 6,200 rpm and 132 lb. ft. of torque at 4,500 rpm (estimated). This Atkinson cycle-type engine reduces pumping loss by delaying the close timing of the intake valve in the compression stroke, therefore maximizing the expansion ratio it is the only Atkinson cycle engine to be combined with multi-port injection in the compact class. This greater expansion ratio is made more efficient by allowing additional energy to be produced. Furthermore, this engine features a high compression ratio of 12.5.

Other enhancements include intermediate valve cam phasing that increases the operational range of the intake valves and helps to reduce pumping loss."

Link

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#4525528 - 09/25/17 08:34 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: JustN89]
4WD Online   confused


Registered: 09/21/10
Posts: 6428
Loc: Texas
Thought the real McCoy (origin Elijah) had a variable stroke - not VVT ... some (good) modern day technology around but does the name hold true?

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#4525530 - 09/25/17 08:38 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: JustN89]
WyrTwister Offline


Registered: 01/13/13
Posts: 1532
Loc: Texas
I did a google search for Atkinson Cycle engine . Read several articles & know a tiny bit more than I did about a Atkinson Cycle engine .

OK , the spark is 100% under control of the computer .

Fuel is 100% under control of the computer .

In an automatic transmission , the gearing is 100% under the control of the computer .

Valves , through the cam phaser , are under partial computer control . If you had the valves actuated by electric / electronic solenoids , you would have them under 100% control of the computer .

You could really get arrive with the software . If you could implememt AI , yhe software / computer could learn to tune the engine for economy , low emissions , torque , max horse power . Or , maybe things I have not thought of .

Wonder is anyone is researching this idea ?

Best of luck to you , :-)
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#4525532 - 09/25/17 08:39 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: JustN89]
skyactiv Offline


Registered: 03/02/13
Posts: 4405
Loc: The Midwest
Mazda uses what they call the Mazda Miller cycle for obtaining an Atkinson cycle on the Skyactiv engines.
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#4525544 - 09/25/17 09:02 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: VetteElite]
2010Civic Offline


Registered: 12/06/14
Posts: 350
Loc: Minnesota
Originally Posted By: VetteElite
If I'm remembering correctly, non-hybrid Atkinson engines use their VVT systems to simulate Atkinson cycle and can switch to the more powerful Otto cycle on demand.


The R18 engine in 2006-2015 Civic's have a simulated Atkinson cycle. On the economy cam profile the intake valve stays open longer and lets part of the air/fuel mixture back out of the combustion chamber. On the "power" cam the intake valves close sooner. This also reduces pumping loses.


Edited by 2010Civic (09/25/17 09:03 AM)
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#4525605 - 09/25/17 09:37 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: skyactiv]
oil_film_movies Offline


Registered: 06/13/16
Posts: 2569
Loc: MN
Originally Posted By: skyactiv
Mazda uses what they call the Mazda Miller cycle for obtaining an Atkinson cycle on the Skyactiv engines.

Its not a Miller Cycle on the Skyactiv engines, unless they have a supercharger, which I don't think they do. Miller Cycles require superchargers by definition.

Nobody runs Atkinson Cycle using the bizarre crankshaft that the original patent in 1887 used. Its always done with late intake valve closing.


As for the original question, the only durability issue I can think of is having the air-fuel mixture washing ('burping back') over the intake valves may cause extra intake valve stem deposits. Potentially you would think.

One more note: The high compression ratios in Atkinson Cycle engines are a little decieving, since late intake valve closing reduces the effective compression stage.
What is nice is that a good VVT system can come and go in and out of Atkinson as conditions dictate.


Edited by oil_film_movies (09/25/17 09:42 AM)

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#4525621 - 09/25/17 09:50 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: WyrTwister]
oil_film_movies Offline


Registered: 06/13/16
Posts: 2569
Loc: MN
Originally Posted By: WyrTwister
You could really get arrive with the software . If you could implememt AI , yhe software / computer could learn to tune the engine for economy , low emissions , torque , max horse power . Or , maybe things I have not thought of . Wonder is anyone is researching this idea ?

Yes engine makers have been using Artificial Intelligence (AI) algorithms to optimize engine operation. Much of this is done off-line, in the lab or field testing, where the engine maps are adjusted to reach optimality goals (performance, MPG, emissions, you know...). Some trimming and adjustments are allowed as the engine is used in real-time, although the algorithms are very limited in authority so they don't diverge in new unknown directions. Actually the 'Integral' (I) part of traditional PID control systems is a trimming adjustment used for the last 30 years in engine control systems, a basic 'learning' adjustment.

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#4525624 - 09/25/17 09:55 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: JustN89]
NateDN10 Offline


Registered: 01/10/10
Posts: 1735
Loc: Rochester, NY
I think one reason that dedicated Atkinson Cycle engines are only used in hybrids is that their specific output (i.e. horsepower per engine displacement) is low. In a hybrid this is fine because the electric motor makes up the difference, but it would require an unacceptably large engine in a non-hybrid.
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#4525691 - 09/25/17 11:28 AM Re: Atkinson Cycle engines on non-hybrid vehicles [Re: NateDN10]
oil_film_movies Offline


Registered: 06/13/16
Posts: 2569
Loc: MN
Originally Posted By: NateDN10
I think one reason that dedicated Atkinson Cycle engines are only used in hybrids is that their specific output (i.e. horsepower per engine displacement) is low. In a hybrid this is fine because the electric motor makes up the difference, but it would require an unacceptably large engine in a non-hybrid.
I'm not sure what you mean by "dedicated" Atkinson when VVT allows it to come and go on the fly, and all operate that way. It may be true hybrid engines do Atkinson more, as a percentage of total running time. All are part-time Atkinson anyway. When we say 'Atkinson', we simply mean those moments when the intake valve closes late, thats all. Nothing more complicated than that. Any engine with a VVT can claim it if it does late valve closing!!

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