Atkins Cycle

[Roker]

For those technical minded I have wondered for awhile.

As my 2ZR FXE engine (Corolla) is Atkins Cycle and has Variable Valve Timing, does it change between Atkins and Ottoman cycle as more demand is required. If not, what other function would VVT be required to do 

[CPN]

Toyota's hybrid powertrain ICE, constantly switches between the Otto & Atkinson/Miller cycles controlled by the system's "brain" in order always to keep the ICE at, or as close as possible to, its peak thermodynamic efficiency dependent on the load that the vehicle is facing. The HV Battery and traction motor MG2 work in conjunction with that to try and achieve the best overall system efficiency.

[Cyker]

It'll switch to Atkins when it feels its a bit overweight, but go back to the Ottoman when it's low on energy...   

 

[AndrueC]

I don't think the ICE in the HSD models switches modes. Least-wise the 1.8 unit in my Corolla doesn't.

My previous car was a Honda Jazz and it definitely did switch (it was a marketed feature) and the performance change was night and day. It was like having a small turbo under the bonnet.

Most VVT systems only adjust the lift timings slightly. Switching to/from Otto/Atkinson is a more drastic change and I don't think many engines do that due to the complexity of handling such a marked difference in power output.

[flash22]

technically it needs a super/turbocharger to be classed as a Miller cycle it's just a https://en.wikipedia.org/wiki/Atkinson_cycle

by using an OCV to advance or !Removed! the cam timing at higher rpm's lowing the compression and making it a cleaner, leaner burn, with the Otto cycle being your bog standard suck, push, bang, blow................

 

and that's how babies are made

[Mjolinor]

Why  would you need the Otto cycle in a hybrid? The Otto - Atkinson loss of power is made up for by the electrics, shirley.

[CPN]

@AndrueC I think that perhaps you may be misunderstanding the Toyota Hybrid system, its "Power split device" and how it all works?

Toyota's Hybrids operate completely differently to any other hybrid in the marketplace. The electric motor doesn't "help out" as you put it. In Toyota's system there are two Motor/Generators MG1 & MG2.

MG1 is the motor/generator driven by the ICE. It is used to recharge the HV Battery and supply electrical current to MG2. It also serves as the engine's starter. MG2 is the drive motor, supplying power to the wheels with or without the ICE's help. (note that last bit in bold)

The Power split device (PSD) is a planetary gear set that removes the need for a traditional stepped gearbox and transmission components. It acts as a continuously variable transmission (CVT) but with a fixed gear ratio.

I'm pretty sure that this type of hybrid powertrain is unique to Toyota Hybrid cars and that Honda's is nothing like it or as efficient.

[CPN]

9 minutes ago, Mjolinor said:

Why  would you need the Otto cycle in a hybrid? The Otto - Atkinson loss of power is made up for by the electrics, shirley.

No. See my post above...

(...and stop calling me shirley! 😉)

The primary reason for the switchover from Otto to Atkinson/Miller (as needed) is to attempt to keep the ICE running at its peak thermodynamic efficiency for as much of the time as possible.

[Rhymes with Paris]

I understand a few simple things about engines, like the difference between 2 stroke and 4 stroke, and vvti.

And I have noticed that a lot of posts refer to the Atkinson and Miller cycles in the same engine.

I was going to ask some kind soul to explain those to me, but just noticed flash22s post so thanks for that.

 

[AndrueC]

1 hour ago, CPN said:

@AndrueC I think that perhaps you may be misunderstanding the Toyota Hybrid system, its "Power split device" and how it all works?

Toyota's Hybrids operate completely differently to any other hybrid in the marketplace. The electric motor doesn't "help out" as you put it. In Toyota's system there are two Motor/Generators MG1 & MG2.

MG1 is the motor/generator driven by the ICE. It is used to recharge the HV battery and supply electrical current to MG2. It also serves as the engine's starter. MG2 is the drive motor, supplying power to the wheels with or without the ICE's help. (note that last bit in bold)

The Power split device (PSD) is a planetary gear set that removes the need for a traditional stepped gearbox and transmission components. It acts as a continuously variable transmission (CVT) but with a fixed gear ratio.

I'm pretty sure that this type of hybrid powertrain is unique to Toyota Hybrid cars and that Honda's is nothing like it or as efficient.

No, I think you're the one who is confused. I'm well aware of how the HSD power split device works. Toyota's HSD has nothing to do with Otto or Atkinson cycle.

The HSD just blends power from the electrical motors and the ICE. How the ICE is operating internally is irrelevant to that part of the transmission.

It's possible that the ICE is also switching between those two modes but I have never experienced any evidence of it. I suspect it would overcomplicate the ECU logic or as another person suggested is just pointless because the electrical motors can make up the difference.

Do you have any actual documentary proof that it can do that? The reason I mentioned the Jazz was to show that I have experience of how the two modes perform.

That tells me that the 1.8 litre engine in my Corolla never operates in Otto mode because it does not have the same raw power that the 1.3 litre in my Jazz had.

 

[AndrueC]

And there's this article from Toyota itself (sorta).

https://mag.toyota.co.uk/how-does-toyota-hybrid-work/

"Is the engine different to that of a normal car?

In short, yes. The internal combustion engine used in a Toyota hybrid uses a slightly different engine cycle than the conventional Otto-type four-stroke cycle. Called the Atkinson cycle, this modified four-stroke cycle produces less heat and is therefore more efficient."

No mention there of it switching between Atkinson and Otto modes.

And following one of the links in that article:

https://mag.toyota.co.uk/toyota-use-atkinson-cycle-engines/

Now granted both are really just marketing articles but if the engine could switch between the two modes they'd surely crow about that as well.

[TonyHSD]

I think the engines that run between two cycles are the MX series on non hybrid set ups like Yaris 1.5 manual, or Corolla 2.0 cvt  available in other countries. 

[CPN]

3 hours ago, flash22 said:

with the Otto cycle being your bog standard suck, push, bang, blow................

My dad always used to call it "suck, squeeze, bang, blow"....

[Extreme_One]

20 minutes ago, CPN said:

My dad always used to call it "suck, squeeze, bang, blow"....

Based on this description I've determined my wife is most equivalent to a 2-stroke. 😏

[CPN]

3 hours ago, AndrueC said:

No, I think you're the one who is confused.

Not at all. I've taken a keen interest in how Toyota's Hybrid system works since I started driving them 10 years ago.

3 hours ago, AndrueC said:

Toyota's HSD has nothing to do with Otto or Atkinson cycle.

That is not true but if you want to split hairs, the 3 & 4 cylinder variants used in the current hybrids are essentially Otto cycle engines but using the fuel-efficient part of the Atkinson cycle (delayed closing of the intake valve during the compression stroke) which is facilitated by hydraulic actuation of the camshaft position. It is only one part of the cycle that is Atkinson (when actuated), the rest is Otto.

3 hours ago, AndrueC said:

It's possible that the ICE is also switching between those two modes but I have never experienced any evidence of it. I suspect it would overcomplicate the ECU logic or as another person suggested is just pointless because the electrical motors can make up the difference.

It is not motors (plural). MG2 is the only motor directly connected to the driven wheels.

3 hours ago, AndrueC said:

Do you have any actual documentary proof that it can do that?

Nothing that I can put my hands on right now but I'll have a look...

3 hours ago, AndrueC said:

The reason I mentioned the Jazz was to show that I have experience of how the two modes perform.

I'm not denying that you do. I have no experience directly of the Jazz.

3 hours ago, AndrueC said:

That tells me that the 1.8 litre engine in my Corolla never operates in Otto mode because it does not have the same raw power that the 1.3 litre in my Jazz had.

I'm surprised by your statement tbh...

[CPN]

Extract from Toyota Magazine...

This revelation allowed Toyota to build the world’s first Otto cycle engine with a simulated Atkinson-type valve action to significantly improve fuel efficiency. Known internally as the 1NR-FXE, the 1.5-litre four-cylinder petrol engine was installed in the 1997 Toyota Prius and paired with the fantastic new Toyota Hybrid System (now known as Hybrid Synergy Drive).

[Mjolinor]

7 hours ago, Extreme_One said:

Based on this description I've determined my wife is most equivalent to a 2-stroke. 😏

All women are the same, they can all do two things at once just like a two stroke.

Sucksqueeze, bangblow.

But also like a two stroke they don't do either efficiently.

[Saxmaniac]

As I understand it, Toyota hsd use simulated Atkinson cycle for greater thermal efficiency, full burn by the end of the stroke, the torque deficit made up via the electric motor (s), mg1 and mg2 can contribute to the drive if all the power is needed. Thinking logically, why would the engine revert to Otto cycle and run far less efficiently when the whole system is designed to use the characteristic of the Atkinson cycle? Plus, there's no mention of this anywhere 

[Roker]

4 hours ago, Saxmaniac said:

As I understand it, Toyota hsd use simulated Atkinson cycle for greater thermal efficiency, full burn by the end of the stroke, the torque deficit made up via the electric motor (s), mg1 and mg2 can contribute to the drive if all the power is needed. Thinking logically, why would the engine revert to Otto cycle and run far less efficiently when the whole system is designed to use the characteristic of the Atkinson cycle? Plus, there's no mention of this anywhere 

The Otto cycle would give more power when required ex . overtaking, why have VVT what is it used for

[Cyker]

Just for some clarity, it's only the hybrids with the 'DynamicForce' branded engines that have the wideband cam phasing ("VVT-iW") which allows switching between the Atkinson and Otto-cycle 'modes'.

The 1.8 is mainly an upgraded version of the same engine the Auris hybrid had and only runs in Atkinson cycle mode, although I think I read somewhere they were going to add the wideband cam phasing to the new '5th gen' versions of it to also allow the mode switching.

Before that, only a few engines could do that switch, e.g. the 1.5L petrol non-hybrid Yaris Mk3 and the 1.2 turbo 8NR-FTS the Auris can have, but AFAIK none of them were hybrids as all the hybrids were Atkinson-cycle only.

 

The main reason for adding the dual-switch is, while the Atkinson-cycle is more efficient, it's really gutless - IIRC the Atkinson-cycle 1.5L cranks out similar torque to the 1L engine in an Aygo - This is partly why the early HSDs gained this reputation for over-revving because they had to rev much higher than a conventional engine to deliver similar levels of torque. I can see why they did it, as on paper it makes sense when paired with a nice torquey electric motor, but they really should have used more powerful electric motors because at higher speeds the electric motors drop off noticeably and the Atkinson-cycle engines don't have the grunt to take up the slack as the electric motors hand over to them at higher loads, and have to rev up to compensate.

 

Otto-cycle is just what every normal petrol engine car uses, and being able to switch to Otto-cycle gives the ECU a lot more options. One of the reasons the Mk4 Yaris feels so powerful is it now has an actual 1.5L engine in it which can deliver real 1.5L engines worth of torque and power (And fuel guzzling  ) on demand - I find it quite noticeable it in mine, when I'm not going full power, but maybe starting to feed in medium beans, the torque will increase but when it switches over from A to O mode, the RPMs will actually drop for a moment even while the torque continues to rise. It's pretty neat, and allows it a lot more shove without getting too noisy and rev-happy, at the cost of fuel economy (At full throttle this thing can get thirsty very quickly!)

 

I just wish Toyota had come up with a better name for it as, pedantically and strictly speaking, it's NOT Atkinson-cycle OR Miller-cycle.

The actual Atkinson-cycle uses a very funky linkage to make the compression and expansions strokes different lengths, whereas the Toyota system and Miller-cycle use valve-timing to simulate different compression and expansion stroke lengths in a less effective but much less failure-prone way to a proper Atkinson-cycle engine.

The Toyota system is much closer to the Miller-cycle mechanically, just missing the supercharger that Miller used to compensate for the dreadful torque.

They should have come up with a stupid marketing name for it like Miller-Electrically Enhanced, or Miller-EE (It's like Miller, so it's Millery, geddit??? I'll get my coat...), or Partial Intake Charge New Induction Cycle, or Super High Up Timing Uniform Pressure...?  

 

[AndrueC]

19 hours ago, CPN said:

Extract from Toyota Magazine...

This revelation allowed Toyota to build the world’s first Otto cycle engine with a simulated Atkinson-type valve action to significantly improve fuel efficiency. Known internally as the 1NR-FXE, the 1.5-litre four-cylinder petrol engine was installed in the 1997 Toyota Prius and paired with the fantastic new Toyota Hybrid System (now known as Hybrid Synergy Drive).

Hmmm. I'm not sure that proves that it can operate in both modes. I doubt anyone has ever built a true Atkinson cycle engine as the linkages are too complicated. It is possible with modern ICE however to simulate Atkinson mode on what would otherwise be an Otto cycle engine and that might be what that article is suggesting.

As I've mentioned a few times the Honda Jazz did that (at least the model I owned) and that tells me that you get a lot more power out of an ICE operating in Otto cycle than you do in Atkinson. That's the only explanation I can offer for why my 1.8 Corolla is 'not a lot' more powerful than my Jazz.

Edit:Well put Cyker. I think in the past I've wondered why Toyota didn't offer Otto cycle for the 2.0. For the 1.8 it makes sense as it's targeted at us sensible folk but the 2.0 would perform like a rocket if it also had Otto cycle up its sleeve and the folks who opted for that version clearly care less about fuel consumption 😉

[CPN]

4 hours ago, AndrueC said:

I doubt anyone has ever built a true Atkinson cycle engine as the linkages are too complicated.

True but it is simulation rather than an actual version... (and even then for only the squeeze part of the cycle...)

4 hours ago, AndrueC said:

It is possible with modern ICE however to simulate Atkinson mode on what would otherwise be an Otto cycle engine and that might be what that article is suggesting.

That is how I interpreted it...

4 hours ago, AndrueC said:

As I've mentioned a few times the Honda Jazz did that (at least the model I owned) and that tells me that you get a lot more power out of an ICE operating in Otto cycle than you do in Atkinson.

Absolutely. It's obvious from what is actually going on in that "simulation". If you keep the inlet valve open for longer during the squeeze part of the cycle, the compression losses would be dreadful by comparison... (with a straight Otto ICE)

4 hours ago, AndrueC said:

That's the only explanation I can offer for why my 1.8 Corolla is 'not a lot' more powerful than my Jazz.

Was your Jazz a conventional ICE or was it hybrid? (not sure if they made one?)

4 hours ago, AndrueC said:

Edit:Well put Cyker. I think in the past I've wondered why Toyota didn't offer Otto cycle for the 2.0. For the 1.8 it makes sense as it's targeted at us sensible folk but the 2.0 would perform like a rocket if it also had Otto cycle up its sleeve and the folks who opted for that version clearly care less about fuel consumption 😉

I can totally back up what @Cyker is asserting. The Mk4 is excellent from 0-30mph (foot flat down) as you are getting the instant torque from MG2 added to the maximum power that the ICE can muster and in that process, a Mk4 will leave many high performance (standard ICE) cars in its wake from a standing start up to 30mph. The 130 powertrain feels even better (I've had both so I can compare directly the behaviour between the two). One of these days, when I find a quiet road, I'll do some standing start tests. I once managed to get 2.8 secs to 30mph out of the Red Baron (Launch Edition 2020) and its 115 unit...

[Saxmaniac]

I don't know where CPN gets the idea from that the 1.8 engine reverts to Otto cycle, I've studied any information I could find about how these things work and there's not a hint of that anywhere, plus I think the engine runs a higher compression ratio which is ok for the reduced charge with the Atkinson cycle but may be too much for Otto cycle?  I think there's some engines on the market that switch between Otto and Atkinson, possibly Mazda do one, not sure 

[AndrueC]

https://en.wikipedia.org/wiki/Toyota_ZR_engine#2ZR-FXE
 

No mention of Otto cycle.

https://www.motorreviewer.com/engine.php?engine_id=155

No mention of Ottocycle.

https://www.torquecars.com/toyota/2zr-tuning.php

No mention of Otto cycle.

And here's a YouTube video of someone converting it to be Otto cycle.

To do it he has to take the engine apart.

All of the above also state that the power output is 98bhp. The 1.3l engine in the Honda Jazz is rated at 100bhp. Either Toyota produce rubbish engines or else something else is in play here.

Can we please stop this nonsense now? The ICE in Toyota HSD runs on a simulated Atkinson cycle. It does not and can not run in Otto cycle.

[rado77]

My few cents here. Yep, 1.8 hybrid works in Attkinson, all the time. Only the vvt system "approaches the otto cycle" in that it opens intake valves sooner. Bigger are rpms, the sooner are intake valves open - and it's very similar to Otto cycle. But it's still Atkinson. In other words - Atkinson cycle opens intake valves later, and closes them later. VVT system (dynamically, based on rpms) opens valves sooner and closes them sooner...like classic Otto cycle engine. If this 1.8 4 cylinder will run in Otto cycle, it will have 150+ HP. But Atkinson cycle is weaker, but everything is subordinated to thermal efficiency and low fuel  consumption (emissions)