Maximum speed with ICE off

[Don Mac]

A tech-curious query -

Does anyone know the maximum speed at which the car will turn off the ICE (e.g. when cruising on a motorway)? Assuming that there is one, I read that it was less than 70mph on the early Prius due to the maximum rpm of its MG1.

Similarly, what is the maximum speed achievable before the ICE cuts in?

[flash22]

It's rpm and load dependent tbh

[TonyHSD]

70mph can do but if you are going downhill. In older hybrids the engine in these scenarios will be idling  at around 1000rpm or little over at 60mph for example. 

[AndrueC]

I thought I'd managed to persuade mine to come on well above 70mph but it's a pretty pointless exercise anyway. Almost certainly not the most efficient use of the electricity in the Battery and won't run very long like that anyway.

[Don Mac]

1 hour ago, TonyHSD said:

70mph can do but if you are going downhill. In older hybrids the engine in these scenarios will be idling  at around 1000rpm or little over at 60mph for example. 

Sounds good, I would get a real geek buzz out of running at that speed with the ICE silent!

As I understand it there is a maximum ICE-off speed (regardless of how steep the downhill gradient is) because the MG2 (drive motor) is permanently connected to the driveshaft (no clutch). This means that MG1 (the starter/generator) has to be spun up to prevent the ICE being turned over when its not running (since MG1, MG2 & the ICE are all connected by the power distribution module). MG1 can only spin so fast before burning out, which determines the speed limit for "sailing".

Did I get that right? I'm fascinated by the technology, but I'm not an engineer.

[Gerg]

Sounds like you need this video:

https://www.google.com/search?q=weber+university+prius&oq=weber+university+prius&aqs=chrome..69i57.10325j0j15&sourceid=chrome&ie=UTF-8#fpstate=ive&vld=cid:e1226a1e,vid:TRSQEgLk_2M

Or maybe one of their other ones.

The MG1 rpm limitation is due to potential centifugal force problems, isn't it?

 

[Don Mac]

I love those opened up & labelled transmissions!

My own searches found this - https://priuschat.com/threads/introduction-to-prius-power-flow.29352/

and this - http://john1701a.com/prius/documents/Prius_Power-Split-Device_details.pdf

That, and binging on "The Car Care Nut" on YouTube - 

is where my, vague, understanding of the Toyota hybrid system comes from.

I don't know exactly what limits the maximum rpm of the motor in this case. It could be the design of its windings and the power supply frequency/current limitations, rather than the mythical "centrifugal force" 😜. I know very little about AC motors, other than that they are a lot cleverer than me...

 

[Cyker]

I think in the previous gen it was something like 30-40mph before the ICE was forced to turn?

Some clever bod thought to put in a reduction gear so MG1 doesn't have to spin as fast in the newer ones; I've managed to get mine to go at just over 80mph without the ICE having to turn.

I should emphasise that this was not the car powering itself to 80mph on MG2 - This was me going down a long hill after overtaking someone and holding the accelerator just enough to stay in the "Eco" part of the power gauge, but not enough to start the engine; Even then the car was still slowly decelerating from air resistance! The electric motors (In my one anyway!) can't really hold the car above 60-ish mph on the flat for very long, and definitely can't accelerate to such speeds on their own (At least without a steep downhill or an apocalyptically strong tail-wind!).

Also this is in the Mk4 Yaris - The Corollas and other hybrids have more powerful electric motors, but also more mass, so results may be slightly different with those!

[Gerg]

33 minutes ago, Don Mac said:

I love those opened up & labelled transmissions!

My own searches found this - https://priuschat.com/threads/introduction-to-prius-power-flow.29352/

and this - http://john1701a.com/prius/documents/Prius_Power-Split-Device_details.pdf

This is very old but maybe some info you've not covered yet.

Analysis Benchmark-Toyota-Prius-3-Système-Hybride-HSD.pdf

[TonyHSD]

Dr. Kelly from Weber auto mentioned something about 16000rpm in gen 3 and up to 19000rpm on later generations. Gen5 now available  could be even higher. Gen 3  max 30mph in ev although in some  cases it gives you a feeling it’s going in ev actually it’s not , the engine is idling but still better  than 2500-3000rpm in other petrol cars. 
The trick driving a Toyota hybrid is to keep an eye on the power meter and energy graphics, sometimes when accelerating you can just ease a bit the throttle and the Battery will help more the engine to propel the car. If you do so you get less noise and higher mpg, and you won’t be too far off if you do that with more throttle, just gonna burn unnecessary petrol. 
When full power is needed, floor it for a short time and release the accelerator, again you will get less engine noise and gather possible acceleration. It takes time and practice to master the accelerator control but pays off later . 😉

[Gray86]

Pretty sure I’ve had around 80mph and the car has dropped into EV mode. Really needs a downhill gradient, and it’s only a brief EV stint. 

[Tech429]

When out on a motorway at around 75mphish you will see the ICE flat-line for about 20 seconds then come back on - but only if on flat or slight downhill... and if not jumping on the throttle... oh and if the Battery is charged sufficiently to run EV.

It also happens when in other speed-limit areas too.