Otto and Atkinson cycle

[Cbatoday]

does the hybrid solely run on the Atkinson cycle to reduce heat and be more efficient or does it switch to the Otto cycle through variable valve timing to create more power in certain conditions

[AndrueC]

It's Atkinson all the way. I've always thought that to be an odd choice but it may be down to the extra complexity of managing a two-state engine which presumably would complicate an already complicated engine map.

My previous car was a Mk3 Honda Jazz and it adjusted the timing to run in Atkinson mode below about 2,500 rpm. Unfortunately in the earlier versions of the Mk3 the transition from Atkinson to Otto wasn't very well handled by the CVT. It's a long story but I think that the CVT was tuned for economy and given the wide choice of ratios available would sometimes go long rather than cause the engine to increase revs. This was most noticeable when pulling away from roundabouts. If you just gently pressed the accelerator the car would barely accelerate. It felt like someone had tied a concrete block to the back. Also going up certain hills the (the A422 up to Steane Park is one @Timmon would know) it was hard to maintain 50mph. If you just kept gradually pressing the accelerator nothing happened until suddenly the ECU decided it had to let the revs rise and you'd get a distinct bump as the Otto cycle kicked in and you'd have to back off. It didn't start 'hunting' but it wasn't what you expect from a CVT equipped vehicle.

I eventually learnt to do a mini kick-down for the roundabout situation - bump the revs straight to 3,000 and the car would move quite nicely. But there was nothing much you could about the hill problem. The face-lifted MK3 appears not to suffer from this from the one time I drove a courtesy car. Another thing Honda did with the face-lift (which I'm in two minds about) is simulate the rise and fall of RPMs at the top end. I'm not sure how they did it because the feel was smooth and steady acceleration as you'd expect from a CVT and the effect was quite pleasing. But somehow it felt like fraudulent way to operate a vehicle with a CVT :-/

[FROSTYBALLS]

Also see https://blog.toyota.co.uk/toyota-use-atkinson-cycle-engines