What limits Yaris IV (or any other Toyota Hybrid) top speed ?

[Stopeter44]

The new Yaris IV can run at up to 80 mph / 130 kph in EV mode, which I presume represents the power limit of MG2 when it only is "driving" ?

I assume that if the car is running at higher speeds higher, MG2 needs the extra torque from the ICE to push the car along at speeds higher. In other words, is it simply real world fluid dynamic laws that limit the cars top speed, or is there a limitation built in to protect MG2 ?

Not that I have any intention to run the car all day flat out!

 

[flash22]

The limitations are the torque and the way the power is transmitted, of course with most motors/alternators you don't want to go outside the rpm of that component's design the HSD is not a conventional CVT either

Older US doc that goes into the technical aspects

http://info.ornl.gov/sites/publications/files/Pub26762.pdf

[Bernard Foy]

I’ve never been able to achieve over 100kmh in my Yaris.

[Yugguy1970]

Yes it's the max rotational speed of the electric motor that is the limiting factor. 

[Yugguy1970]

You've never gone avo

4 minutes ago, Bernard Foy said:

I’ve never been able to achieve over 100kmh in my Yaris.

You've never got over 60mph?  Something seriously wrong there if that's true and not a typo?

[Bernard Foy]

11 minutes ago, Yugguy1970 said:

You've never gone avo

You've never got over 60mph?  Something seriously wrong there if that's true and not a typo?

Not on the traction Battery and only seldom do I get that. I’ve often gone over 70mph but never on the traction Battery alone. Absolutely nothing wrong with the car, it’s a super little bit of modern machinery.

[Stopeter44]

2 hours ago, flash22 said:

The limitations are the torque and the way the power is transmitted, of course with most motors/alternators you don't want to go outside the rpm of that component's design the HSD is not a conventional CVT either

Older US doc that goes into the technical aspects

http://info.ornl.gov/sites/publications/files/Pub26762.pdf

Thanks for that Link, it is very dense it will take me a while to go through that!

 

2 hours ago, Yugguy1970 said:

Yes it's the max rotational speed of the electric motor that is the limiting factor. 

It's what I surmised.

 

2 hours ago, Bernard Foy said:

Not on the traction battery and only seldom do I get that.

Well, I imagine to get 80 mph / 130 kph, if only for a moment, you need a full Battery and ideal conditions, like downhill and a following wind.

[MikeSh]

2 hours ago, Yugguy1970 said:

Yes it's the max rotational speed of the electric motor that is the limiting factor. 

Specifically it's the rotational speed limit of MG1 - the smaller one that is on the planet gearing with the ICE.

When the engine is stationary MG1 is being spun by the road wheels and because of the gearing MG1 is going even faster. To prevent over-speed the ICE has to be started to turn the planet carrier and effectively reduce the gearing.

In the first generation the limit was about 30mph. In the second a reduction gear was introduced along with motors with higher possible speeds (IIRC MG1 went from ~6,500 to 10,000 rpm) which lifted the 'no engine' to about 60mph. They have no doubt continued to improve that (we are on 4th gen now).

Since gen 1 at 30 it's very unlikely that the car can be powered at these speeds on the level, but it does mean that when coasting at or slowing from higher speeds the car can go into EV mode much earlier.

[Gerg]

This link is quite a contrast to the link flash22 posted above.

It's written by a really enthuiastic owner of a (then new) mk1 Prius, who has then gone on to find out all he can!  There have been some changes to the design since, but nothing to alter the basic concepts.

https://prius.ecrostech.com/original/PriusFrames.htm

Maybe you haven't seen the excellent Weber University transmission strip-downs?  If so, it's well worth having a look at (one of the many) in this link:

 

 

[Yugguy1970]

Been reading about the Porsche Taycan which has a revolutionary TWO gears in its box.

[Cyker]

You'll struggle to accelerate past 50 with MG2 alone unless you are *really* patient - ICE power is still king there.

However, I find the car will happily switch the engine off and run on MG2 alone once you get to most speeds and stop accelerating, but as you get to 65-68-ish you need to be going on increasingly downhilly parts to keep within the torque limit of MG2 or the ICE will kick in again. I have had it coast down from ~80mph on MG2 alone 'tho after overtaking someone.

 

[Roy124]

8 hours ago, Cyker said:

 

... The car will happily switch the engine off and run on MG2 alone once you get to most speeds and stop accelerating, but as you get to 65-68-ish you need to...... keep within the torque limit of MG2 or the ICE will kick in again... 

 

Which nicely explains why it can be most efficient if you are not in a hurry to cruise in lane 1 at truck speeds.  When doing over 300 miles I really needed to cruise at 70 which really sucked fuel and reduced EV time to a minimum. 

The practical difference was 52 mph average versus a normal 33.  Over a 50 mile journey the difference would be only around 20 minutes. Plan ahead, have a relaxed journey. 

[Stopeter44]

12 hours ago, MikeSh said:

Specifically it's the rotational speed limit of MG1 - the smaller one that is on the planet gearing with the ICE.

When the engine is stationary MG1 is being spun by the road wheels and because of the gearing MG1 is going even faster. To prevent over-speed the ICE has to be started to turn the planet carrier and effectively reduce the gearing.

<snip>

Since gen 1 at 30 it's very unlikely that the car can be powered at these speeds on the level, but it does mean that when coasting at or slowing from higher speeds the car can go into EV mode much earlier.

Do you have a typo in that post ? "When the engine is stationary MG1 ... ", shouldn't that be MG2 ? As I understood it MG2 was always connected to the wheels and spun, though a reduction gear (MG2>Wheels) in direct proportion to road speed. I also thought that MG1 was on the "Sun" gear and the ICE on the planetary gears ? In any case, there are times when any two motors spinning at the right speed will mean that the other one is stationary, or at least that's how I understood it.

22 minutes ago, Roy124 said:

Which nicely explains why it can be most efficient if you are not in a hurry to cruise in lane 1 at truck speeds.  When doing over 300 miles I really needed to cruise at 70 which really sucked fuel and reduced EV time to a minimum. 

The practical difference was 52 mph average versus a normal 33.  Over a 50 mile journey the difference would be only around 20 minutes. Plan ahead, have a relaxed journey. 

I'm a bit confused. You mean drive fluidly, and give yourself some margin of error and the fuel economy would be better ? I cruise on the Autoroutes here at a nominal 110 kph, the limit in France being 130 kph.

Driving faster means more stress, and ultimately difference in time over say a 100 km trip is just 8 mins. I believe means about 1 litre of fuel spent, too. We have toll roads here, so being able to use the "hands free" lane at the toll booth saves a few minutes, over that too.

[Roy124]

17 minutes ago, Stopeter44 said:

 

I'm a bit confused. You mean drive fluidly, and give yourself some margin of error and the fuel economy would be better ? I cruise on the Autoroutes here at a nominal 110 kph, the limit in France being 130 kph.

Driving faster means more stress, and ultimately difference in time over say a 100 km trip is just 8 mins. I believe means about 1 litre of fuel spent, too. 

Sorry if I confused you but that is what I meant. 

[Stopeter44]

And I meant 1 litre less fuel used, too.

[MikeSh]

57 minutes ago, Stopeter44 said:

Do you have a typo in that post ? "When the engine is stationary MG1 ... ", shouldn't that be MG2 ? As I understood it MG2 was always connected to the wheels and spun, though a reduction gear (MG2>Wheels) in direct proportion to road speed. I also thought that MG1 was on the "Sun" gear and the ICE on the planetary gears ?

You are correct, but there's no typo.

As you say MG2 is permanently connected to the road wheels. The ICE is connected to the planet carrier, so when it's stopped the planet gears can still spin on their axles.

The ring gear of the MG1/ICE planetary set* is also permanently connected to the road wheels.

So if the car is moving MG2 and the ring are turning. If the ring is turning and the ICE/carrier is stopped then the ring drives the planet gears which drive the sun gear and thus MG1 is turned. (This is an up-gearing because the ring always has more teeth than the sun gear.) If MG1 was stopped then the ICE would turn.

When the ICE is running it drives the carrier in the same direction as the (car forward) ring direction, thus slowing down the rotation of the individual planets and hence the sun/MG1.

( * Be aware that on the 2nd and 3rd gen (I think) HSDs the MG2 reduction gear is also a planetary system, so don't mix them up.)

[Stopeter44]

@MikeSh Your post is a neat synopsis of how it all works, I don't think I've seen it so concisely put before. I'd over simplified some things notably the planet carrier (in italics in your post for emphasis) I had mushily pushed the planets and the planet carrier together in my "picture" of everything. 

So, it is indeed the rotational limits of MG1 that set the limit for top speed, but as in most all engineering it's a carefully considered compromise, and let's face it just who is going to drive the car, for any length of time at > 160 kph ?

[Cyker]

To put it more simply, MG1 has to spin the other way from MG2 to keep the ICE stationary, and if you're going too fast, MG1 can't counter-spin fast enough against MG2 so the ICE *has* to spin as well.

 

Driving at truck speeds has the big advantage that it's well within MG2's limits, so it can even push the car up gentle hills. Also, when the ICE does have to spin up it doesn't have to for as long, as only a fraction of its output needs to drive the car at truck speeds, and the rest can charge up the traction Battery until it can shut off again and foist its duties back onto MG2 again  

I'm way too impatient for that tho' - I prefer to drive faster and coast down, a sort of less efficient pulse and glide technique  

[TonyHSD]

Interesting reads, my simple answer to the question what limits Toyota hybrids to go further and faster on electric as addition to the all been said it’s the Battery. Electric motors and drive train are capable of doing a lot more however the Battery is very small and can not provide enough charge for long. 

[Stopeter44]

9 minutes ago, TonyHSD said:

Electric motors and drive train are capable of doing a lot more however the battery is very small and can not provide enough charge for long. 

Good point, Tony. I was thinking just "instantaneously".

[preperationlaunch]

The previous hybrids do get around some of the limitations of MG1's top speed, by using MG1 to spin the ICE, rather than running the ICE. To offer almost EV coasting with the engine providing minimal resistance.

In the Mk3 Yaris, at light load or coasting above the 45ish mph cut-off for EV mode, and where conditions permit, MG1 is used to spin the ICE. I've heard it's about a kilowatt or two of power according to some of the prius folks. This stops MG1 from spinning too quickly the other way, whilst reducing fuel consumption/engine drag.

The engine does the following to make it as low resistance as possible:
- Drops engine RPM to 950 rpm, spun by the electric motors
- VVTI timing is retarded as far as possible to reduce the impact of the engine sucking against the throttle flap
- Fuel injection is cut entirely

This mode can be used with what some folks call warp-stealth, where you're feathering the throttle so that regen braking isn't kicking in, and you're not drawing too heavily on the Battery. You can notice that the cruise control will trigger it too, especially on slight downhills.

[TonyHSD]

12 minutes ago, preperationlaunch said:

The previous hybrids do get around some of the limitations of MG1's top speed, by using MG1 to spin the ICE, rather than running the ICE. To offer almost EV coasting with the engine providing minimal resistance.

In the Mk3 Yaris, at light load or coasting above the 45ish mph cut-off for EV mode, and where conditions permit, MG1 is used to spin the ICE. I've heard it's about a kilowatt or two of power according to some of the prius folks. This stops MG1 from spinning too quickly the other way, whilst reducing fuel consumption/engine drag.

The engine does the following to make it as low resistance as possible:
- Drops engine RPM to 950 rpm, spun by the electric motors
- VVTI timing is retarded as far as possible to reduce the impact of the engine sucking against the throttle flap
- Fuel injection is cut entirely

This mode can be used with what some folks call warp-stealth, where you're feathering the throttle so that regen braking isn't kicking in, and you're not drawing too heavily on the battery. You can notice that the cruise control will trigger it too, especially on slight downhills.

Top One ☝️. I can sense all that happening while I am driving, it’s so cool and it pays off driving without music 🎵., for ice once I was using an app for android as recommended by another member and the app gives live info and you can see the engine stays at 1000 rpm while cruising on motorway with very light load and around 55-60mph. 👍 Thanks for the explanation 

[MikeSh]

1 hour ago, preperationlaunch said:

The previous hybrids do get around some of the limitations of MG1's top speed, by ...

... on the battery. You can notice that the cruise control will trigger it too, especially on slight downhills.

For those who have (just about) got their head round the mechanics of HSD, now start thinking about the software controlling it all 🤪

[preperationlaunch]

41 minutes ago, MikeSh said:

For those who have (just about) got their head round the mechanics of HSD, now start thinking about the software controlling it all 🤪

It gets irritatingly clever. I believe the car will actually lug the engine using a combination of motors and throttle control for better efficiency in certain situations.

It's all magic really.

[Stopeter44]

3 hours ago, MikeSh said:

For those who have (just about) got their head round the mechanics of HSD, now start thinking about the software controlling it all 🤪

Yes, exactly ! I'm not even going to try !!