Atkinson S 1.8 Engine

[Wayne2015]

Out if interest...

How does the 1.8 Engine on it own with start/stop on a Prius/Auris compared with the 1.8 Hybrid?

Same 100bhp?

Or equivalent 136bhp?

If they are that efficient does Toyota have them in other low performance/greener models?

[FROSTYBALLS]

The new 1.2T litre engine introduced in the 2015 facelifted Auris, and the re-worked 1.0 litre engine introduced in the new Aygo in 2014, both contain technology which allows them to move from the Otto cycle to the Atkinson cycle. See -

http://blog.toyota.co.uk/new-toyota-1-2t-engine

[Heidfirst]

Out if interest...

How does the 1.8 Engine on it own with start/stop on a Prius/Auris compared with the 1.8 Hybrid?

Same 100bhp?

Or equivalent 136bhp?

Afaik the 1.8 Atkinson cycle engine is not available in anything other than a hybrid. By comparison the 1.8 Valvematic (Otto cycle) produces 147bhp in it's latest incarnation.

[Wayne2015]

Cheers both !

Just intrigue that if the Atkinson engine is that efficient -

And we are all trying to save money (at expense of performance) -

Then why the engine not more common in other models / cars?

And was wondering how much increased in MPG does the motor alone help the overall hybrid cars...

[MEP's Yaris GS]

Cheers both !

Just intrigue that if the Atkinson engine is that efficient -

And we are all trying to save money (at expense of performance) -

Then why the engine not more common in other models / cars?

Because it has very little power output and has to be combined with a hybrid electric setup in order for the car to move.

[Wayne2015]

Cheers both !

Just intrigue that if the Atkinson engine is that efficient -

And we are all trying to save money (at expense of performance) -

Then why the engine not more common in other models / cars?

Because it has very little power output and has to be combined with a hybrid electric setup in order for the car to move.

But surely if it can produce 100bhp on the 1.8 Hybrid -

and the 1.0 Yaris only has 68bhp and the 1.33 Yaris has 101bhp -

Then its do-able?

[TomdeGuerre]

That Toyota blog about the new 1.2 engine is a bit misleading. They give the impression that delaying the closing of the inlet valve only happens in the Atkinson cycle when in fact IC 4 stroke engines have featured overlap in valve timing for yoinks now. As you'll see in the valve timing chart, they do delay it significantly to 105 deg after bottom dead centre. Makes me wonder what's happening to the inlet flow when it's doing that.

[MEP's Yaris GS]

Cheers both !

Just intrigue that if the Atkinson engine is that efficient -

And we are all trying to save money (at expense of performance) -

Then why the engine not more common in other models / cars?

Because it has very little power output and has to be combined with a hybrid electric setup in order for the car to move.

But surely if it can produce 100bhp on the 1.8 Hybrid -

and the 1.0 Yaris only has 68bhp and the 1.33 Yaris has 101bhp -

Then its do-able?

Not really no, the way the load is put through the engine in a hybrid is different to a conventional car. You've even confirmed, BHP to CC on a Atkinson engine is pitiful.

Lots of info about it on Wiki when I looking into it a while back.

[YarisHybrid2016]

Atkinson efficiency comes from the modification to compression ratio and valve timing. It results in reduced power output and reduced torque. Overall, less fuel is consumed per stroke.

By combining the Atkinson cycle engine with the characteristics of an electric motor (and this is where the real advantage of the Hybrid is), then you can make up for the deficiency in the Atkinson cycle.

The electric motor is probably the most mis-understood part of a Hybrid. It has very high torque at low RPM, and due to the way the electric motor and petrol engine outputs can be combined, you don't actually lose any performance, whilst gaining the advantage of increased torque from the electric motor (if you compare the torque output of a Hybrid against a regular petrol powered car, it has significantly greater torque closer to that of a diesel powered car of similar size).

A nice explanation here of the differences:

[Cyker]

It's not the BHP that is the problem, it's the torque. The Atkinson cycle engines have incredibly poor torque characteristics which would make them horrible to drive.

This is why when you put any load on a HSD with no electrical charge the engine screams up to high RPM - It doesn't do this because this is an efficient thing to do, it does this because it needs the high RPM to be geared down into torque.

The engines aren't actually true Atkinson engines as, in real ones, the cylinder moves up and down only a small amount during intake, but moves a lot more during the power stroke to extract more power.

Toyota fake it by extending the intake stroke valve timings so that some of the intake air is actually pushed out - In effect the 1.8L engine sucks in 1.8L of air-fuel mixture, but then pushes back out, say 0.6L, so in effect it's only taken in 1.2L of charge.
It then blows this up normally, but instead of the piston only going down 1.2L's worth of distance, it goes down the full 1.8L which allows it to extract more energy from the power-stroke.
It's clever as this long power stroke is partly why diesels tend to be much more efficient than petrol. Why is the Atkinson cycle so gutless then you might ask?
Well in a diesel, you still have a full cylinders worth of fuel and air combined with that long power-stroke, whereas in this cycle you only have a partial charge.

Pedantic note: This extended valve-timing is more similar to a Miller-cycle engine than an Atkinson cycle, just without the super-charging.

It was pretty clever of them to combine it with an electric motor, as they both cover each others weaknesses - The low energy capacity of the electrics is covered by the large energy capacity of petrol, and the weak torque of the ICE is covered by the strong torque of the leccy motor! (Electric motors are awesome - You get max torque from 0 up to the redline! :D)

I'm interested to see how they get over the low torque in this up-coming 1.2T. I suspect it switches between Otto and Atkinson/Miller mode as needed rather than running in partial-charge mode all the time...


Personally, I think direct drive electric motors are the way forward, with ICE's being reduced to being range-extenders until someone thinks of a better way of storing electricity. Smaller and simpler ICE's with no need for variable gearing or transmissions and diffs or complex pipework, just run at one RPM, tuned for emissions and mpg.

In my head I'm tootling along quietly in my AWD independently torque-vectored leccy car, but when I want to overtake I push this big red button and a nice turbine sound like in Mad Max spins up and then WOOOSH! :D

You hear that car manufacturers? Make that happen!!!

[TomdeGuerre]

i think the technical merits of the Atkinson cycle are being over stated. Only a few of the original Atkinson cycle engines were ever made and they were run in a test facility and only at relatively low RPM. Let's say the modern engine is running at 5,000 rpm. The intake valve opens once every two revolutions (720 degrees) and let's say it stays open for 250 degrees. That means that there are 470 degrees between when the intake valve closes and when it opens again. At 5,000 rpm it will take the engine 0.012 seconds to turn one revolution, and 470 degrees is about 1.31 revolutions, so it takes 0.0156 seconds between when the valve closes and when it opens again. That's a very short space of time to get all the benefits that are being claimed.

As you say the Miller engine is virtually the Atkinson with a supercharger and Mazda developed some with good power results but poor fuel economy - and very expensive to repair when things went wrong. That's what Toyota are doing with their 1.2 turbo engine. I'm very sceptical of how they're going to fare in the real world, only time will tell.

[johalareewi]

This is why when you put any load on a HSD with no electrical charge the engine screams up to high RPM - It doesn't do this because this is an efficient thing to do, it does this because it needs the high RPM to be geared down into torque.

Part of the high RPM is used to generate electricty for the electric motor to provide the torque.

If the HV Battery doesn't have enough oomph for the electric motor (or it can't supply oomph fast enough), the ICE revs a bit more to generate the extra electricity.

[Cyker]

Well, if it is just switching between Otto and Miller/Atkinson then it should be fine - They have enough experience with VVTi that it would be trivial to move the valve timings even more, and if anything the HSD's have shown that the extended valve timings haven't impacted reliability.

The trick is going to be the ECU and controlling which mode to go into and when! You can bet that a 1.2 on a partial charge is going to be painfully gutless so they will have to manage that carefully so it doesn't make the car horrible to drive!

The existing 1.0VVTi is surprisingly nice to drive - Being a DERV person I do find the lack of torque after the initial launch a bit of a let down, but like most jappy engines it wants to rev to produce power and it is very willing to do that