The Atkinson Engine

[B&J]

Can one of the many knowledgeable contributers to this forum explain how the ICE starts so smoothly?

All my previous experience with petrol engines is, of course, a few second cranking from the starter motor before it bursts into life (or flattens the Battery if it's a Ford 100E van).

However, in the Prius, whenever the engine is required, it just starts - no vibration, no fuss, no bother. And it's instant.

I do know that the ICE is an Atkinson cycle engine, which differs from the usual pure Otto cycle. How does it do this and why does it seem so different to other petrol engines, please? Does it mean the ICE is always rotating, ready to fire up when needed? (But there's no starter motor when first starting the car in the morning).

Thanks

B&J

PS : Just thought. Other cars that have Stop/Start technology e.g. VW Bluemotion don't have Atkinson cycle engines. Indeed, the VW is a diesel. Puzzled!

[ian rooke]

Hi the Ice is started by the high voltage motor which spins faster than a normal starter motor also I believe that the valves are open so no compression to slow the ICE getting to speed.

[acetip]

If you do a search for Atkinson engine you get get plenty of info on the principle of how it works.

[Grumpy Cabbie]

It's pretty much as Ian above says. A normal starter motor isn't strong enough to start the car instantly. The motor that starts the Prius/Auris hsd is strong enough to power the car upto a good speed, so spinning an engine doesn't take that long. It also has masses of torque and it's instantly available and always connected to the engine via the hybrid system (which replaces a normal gearbox/transmission). A starter motor on a normal car is weaker, much weaker in comparison and also has to physically engage and disengage.

Hope that helps?

Other cars with start stop use a traditional starter motor, though apparantly an uprated one, so they will start and stop quicker than normal but nowhere near as quick as a Toyota hybrid. Personally I can't see these start stop systems lasting long term if they are used heavily in towns and also the 12 volt Battery will be put under a lot of stress in winter start stop driving. Remember your lights, radio, heater fans etc will all still be running when the engine is off. If you have a 'start/stop' system then I can see these causing big headaches. The hybrid system however, uses the High Voltage 500v (or whatever it is) Battery which being rated at 1.5 kwh (that's 1500w for an hour!) is more than powerful enough to run 100w of headlights for hours! A 12v in a BMW won't.

The electrically driven a/c on the Prius/Auris hsd is rated at 4 kwh at peak output and the HV Battery is happy to power this - though maybe only for 15 minutes at peak, before switching the engine on. I wonder if there is a similar system on start/stop systems to switch the engine on to stop the 12v getting too low? I doubt it.

[timberwolf]

Grumpy, I think you are thinking of the A/C Voltages? The HV Battery is usually quoted as having a nominal 201.6 V D/C I don't why that number sticks in my head - wish I could remember telephone numbers or my passwords as easily! :)

[Grumpy Cabbie]

Grumpy, I think you are thinking of the A/C Voltages? The HV battery is usually quoted as having a nominal 201.6 V D/C I don't why that number sticks in my head - wish I could remember telephone numbers or my passwords as easily! :)

It's something like that but I couldn't be a**ed to look it up. I was meaning it is more powerful than 12 volts.

[Cyker]

Conventional start-stop systems are not set up like normal starter motor setups and they are equipped with beefier motors and batteries to account for the extra use so (Assuming some thought went into the design) it should last as long as a normal system.

The smooth starting of the Prius engine has nothing to do with the Atkinson cycle; It's all down to the very clever HSD gearing setup - The whole thing is basically a planetary gear system like you'd get in the old good automatics and the same reason those old automatics had smooth seamless shifts is the same reason the HSD can spin up the ICE without the associated jerkiness. :)

That and the very powerful electric motor as others have mentioned!

[kithmo]

Conventional start-stop systems are not set up like normal starter motor setups and they are equipped with beefier motors and batteries to account for the extra use so (Assuming some thought went into the design) it should last as long as a normal system.

That's what I thought. I'm not familiar with the current generation of stop/start systems but I seem to remember that the early ones had an electric motor combined generator (alternator) somewhere in the flywheel area, totally different to a conventional starter motor.

Interestingly, according to Wikipedia, Toyota was one of the first manufacturers to implement this in the mid 70's in a Toyota Crown.

See: http://en.wikipedia.org/wiki/Start-stop_system

[Terry953]

Conventional start-stop systems are not set up like normal starter motor setups and they are equipped with beefier motors and batteries to account for the extra use so (Assuming some thought went into the design) it should last as long as a normal system.

My experience with a stop/start [Toyota Optimal Drive] Yarns courtesy car was that if any high electrical power was demanded during the 'engine stopped phase' this resulted in the engine starting on it's own so that the accessories would run off the alternator as usual.

This was demonstrated during the summer and having the Air Conditioning on, stopping at some traffic lights the engine stopped but only for a short time as it fired up on its own before the lights had changed. Presumably this would occur with heater, lights, or other high demands on the Battery during winter.

[Terry953]

Conventional start-stop systems are not set up like normal starter motor setups and they are equipped with beefier motors and batteries to account for the extra use so (Assuming some thought went into the design) it should last as long as a normal system.

My experience with a stop/start [Toyota Optimal Drive] Yarns courtesy car was that if any high electrical power was demanded during the 'engine stopped phase' this resulted in the engine starting on it's own so that the accessories would run off the alternator as usual.

This was demonstrated during the summer and having the Air Conditioning on, stopping at some traffic lights the engine stopped but only for a short time as it fired up on its own before the lights had changed. Presumably this would occur with heater, lights, or other high demands on the Battery during winter.

[Grumpy Cabbie]

Good ol' Wiki to the rescue with an explanation;

http://en.wikipedia....art-stop_system

Note the section at the bottom 'Concerns'. Confirms my worries about 12 volt Battery hammering.

[Parts-King]

The starter runs all the time on stop/start systems, the system doesnt come under too much extra strain as the load is sensed, and if required, re starts the engine. I havnt seen too many problems with stop/start technology and certainly no extra Battery sales!

Kingo

[Grumpy Cabbie]

The starter runs all the time on stop/start systems, the system doesnt come under too much extra strain as the load is sensed, and if required, re starts the engine. I havnt seen too many problems with stop/start technology and certainly no extra battery sales!

Kingo

Maybe true on Toyota versions but my confidence in the system from Fiat et al would be erm, low to say the least.

I hear what you say about Battery issues but the start/stop only applies to the smaller vehicle so far which are generally lower mileage second cars, and they've only been out for a year or so. Give it 40,000 miles and I bet you might.

Kingo, how exactly does the Toyota stop/start system work? You say it's always runs? Is it on a clutch or similar? Or is it on the flywheel etc?

[kithmo]

Good ol' Wiki to the rescue with an explanation;

http://en.wikipedia....art-stop_system

As I pointed out yesterday....

[Grumpy Cabbie]

Good ol' Wiki to the rescue with an explanation;

http://en.wikipedia....art-stop_system

As I pointed out yesterday....

And as I have read and also posted your link, but what it refers to a number of different systems but doesn't specify which one Toyota use, hence my question to Kingo :)

Some use a combined alternator and starter, some use a traditional starter motor, some detect which piston to fire for quicker starting, some use a super capacitor etc etc etc.

Again I appreciate you drawing me to your link but I'll ask Kingo if he could clarify which exact system is used by Toyota and what plans they have for the future of this technology. Do they need a larger capacity 12 volt Battery? Are there any plans to introduce it to automatic models other than hybrids or will hybrids effectively replace the traditional automatics?

[B&J]

Sorry for late reply - have been away for a few days.

Thank you to everyone who's contributed to this; it's a fascinating topic. Had a long trip in an Insight recently, and the start/stop is crude compared to the Prius with very noticeable noise and vibration.

So glad I bought the Prius!

B&J