The most misunderstood aspect of the Toyota hybrid synergy drive system

Ah, thanks. Not sure if I missed that or just ignored it. Like so much of what he says it was clearly tangential - when the claim is that the car will behave a certain way in D when it can't regen any more, observing its behaviour while it's giving the "normal amount of regen" is totally irrelevant to that claim.

 

Oh, he did say that, didn't he? Good catch. He didn't report anything that happened when he ran out of regen—neither engine braking, nor sudden speed runaway—because he never ran out of regen. Hill too short, or didn't start with battery full enough. So it simply wasn't a test of any of the claims in question. I gave too much credit.

With any luck, the upcoming hill in BC will be big enough to be a test, and maybe he'll approach it more seriously.

 

From my searching this discussion in THIS forum alone has been happening for about two decades. Leave the dead horse alone.

When I saw this thread first pop up I thought by OP posting that video people would come to a consensus, that being "information is limited, a well informed technician has told us what he could discern from official toyota internal info, we will use it according to his recommendation".

But here we are, 5 pages of yap yap yap yap yap yap yap yap yap yap based on a 3 year old video of a mode that will almost never get used except for a tiny percentage of people who think they'll need it when they really won't. If a 2001 nissan altima can get down the paved mountain road just fine without its brakes exploding then so can the prius. And I've said this before, brakes and rotors are cheap and we already barely use ours so if they get a little toasty on a downhill excursion oh well. The car isn't going to die, your brakes aren't going to catch fire, you will live and be fine and your family will not die. Your battery will not explode. Outside of a few weirdos who are going to use B mode for daily driving most of you are not going to touch it. Pay attention to the road, don't be a bunch of distracted drivers watching your battery levels and listening for engine noises.

 

There are also thermal parameters that ( can ) mimic the non-plugin behavior in the Primes.
It just makes understanding B mode that much more difficult when trying to describe How B mode works while driving a plugin.
EV modes B mode has never spun the engine for me as long as I haven't run the engine prior to switching to B mode, even in sub 0 F temps. ( not that I'd recommend doing that, but I have in the past.
On the other hand if running the engine through the warmup cycle during a drive session, than switching back into EV mode, one condition that will almost always spin the engine ( and usually at high RPM when speed is above about 35 mph ) is when engine coolant temps have dropped enough (certainly below around 60 F ) switching to B mode will often ( unexpectedly ) spin the engine, and usually run it through another warmup cycle.

There are also other ways a driver can get the plugin to spin the engine. Switching modes between EV and HV is a big one. For me these are all unexpected mistakes I've made shifting to B at the wrong time and spinning up the engine.

I've never had the common, decent fully charged plugin engine spin up, as I have to climb a 1/10 mi 50 ft pretty steep incline to get out of the neighborhood anywhere from 3/10s to 2 miles away from home.

 

I guess you haven't been here long enough to read posts from a few members who relied on advice such as yours, and did end up having their brakes overheat enough to require repair or replacement. That cases that come to mind had descents of 3,000 and 3,500 feet.

That Nissan Altima has a much larger engine than any Prius, which helps with engine braking when properly downshifted.

 

That much is true; the discussion has been happening in this forum for that long, but more productively than you've let on here. Participants had considerably fleshed out the "limited" published information already, before this thread appeared.

It's been well understood for a while now. Car Care Nut's top-line recommendation agrees with what was already understood, so yes, "use it according to his recommendation" is sound advice. The rest of Car Care Nut's video doesn't explain things as well as PriusChatters already had, so the video is ok but there's better information to be found on this site.

The "yap yap yap" you're seeing here is chiefly one newcomer to the forum seeking to portray what was already well understood as mere 'guesswork' and 'speculation', and various people, who already understood it, responding to that newcomer. That sort of thing happens on forums from time to time, and feels unproductive, but doesn't mean none of the earlier work was ever productive. And sometimes (sometimes), even the effort of having to explain it again turns out productive too, such as if a newcomer is really genuinely struggling with a particular detail, and a better way to demonstrate it is found.

 

You are placing way too much importance in the engine braking capabilities of passenger sedans. It's not that deep. And most are automatics anyway. Family vacay drivers aren't out there downshifting to engine brake.

And OH MY GOD SOMEONE HAD TO REPLACE THEIR PADS AND ROTORS IN A PRIUS AT 125k MILES INSTEAD OF 150k MILES BECAUSE THEY DID SOME EXCESSIVE DOWNHILL DRIVING. OH THE HUMANITY!

You guys are so weird. Prius drivers really do earn some of the bullying they get on the road. And I say that as an owner of one.

 

I've read through a few of these treads now and I think the key difference is the Prime vs non-Prime aspect.

For instance, I wonder if because the Prime has a larger battery, if it can absorb more through regenerative braking than the standard Prius. Usually the larger the battery pack, the more current you can pull/push. Maybe the Prime can slow the car down more via regenerative braking and doesn't need to rely on the motor as much? This would mean you'd need to find a larger hill to get the engine to come on in D mode.

On the other hand, the motors are the same for both versions so perhaps there isn't a difference in this manner.

Of course, I'd think all this should be moot if the pack is full. I wish I had a suitable hill near me to test this out on my Prime...

 

Absolutely. That's been covered above, and of course is the reason the Prime owners' manual has the "Regeneration Boost" section, like a new Toyota pun on "B", which definitely does not stand for that in a non-Prime.

"more current you can pull/push" could mean stronger regen (or a steeper hill regen can hold your speed on). Maybe not without a bigger motor.

But even without stronger regen, the larger battery totally means you can keep up the same regen rate for a much longer time. A much longer downhill before anything besides regen is needed.

 

The battery in the hybrid can't supply the energy to get full output from the traction motor. Need the other motor generating the balance with the engine's help. The inverse of that means the battery can't take in the full amount the traction motor could generate through braking.

The bigger battery of the plug in negates that energy limit in both directions.

 

That isn't even remotely close to what those members described.

Do you project much?

 

And the motor output has been beefed up too in the plug-in, according to specs - 163kW 120kW rather than 113kW 83kW. Maximum AC voltage also raised from 600V to 650V. It's possible that means a corresponding boost to the regen ability, raising the motor limit too.

 

For those of us coming from Gen3 Liftbacks -- which the OP claims to have previously owned (though maybe with another in between) -- the brochure lists an electric motor power of 60 kW, but a battery power of only 27 kW. Though Chap seems to have found regen limited to ~13 kW.

Either Prime is a huge electric power boost from that.

 

Oops, my bad. Those 163 and 113 were horsepower numbers. That should have been "120kW rather than 83kW".

"Battery power" seems easiest to compute (estimate a lower bound for at least) as "max combined output minus max engine output", which would give that 27kW for the G3.

Corresponding computation for G5:

G5 HEV has 83kW motor with at least 33kW battery power
G5 PHEV has 120kW motor with at least 53kW battery power

(But it's possible the battery power usable in EV mode is actually higher on the PHEV, if there's another limiting factor on the combined output)

 

My RAV4 has a 177 hp gasoline engine, but a combined system power of 302 hp. That is 125 added hp from the battery, or 93 kW.

I believe I have seen a larger EV-only power rating, but can't dredge that up at this instant.

 

Computing from the Prius plug-in's EV mode acceleration (0-60 in 10.5s), you get a similar number:

60mph = 26.8 m/s

Final kinetic energy = 1/2 * 1580kg * (26.8m/s)^2 = 0.57 MJ

Average power (ignoring drag!) = 0.57MJ / 10.5s = ~54kW.

Given drag, and assuming the output isn't totally flat, the peak must be somewhat higher.

Same computation for the RAV4 (0-60 in 9.5s):

1/2 * 1920kg * (26.8m/s)^2 = 0.69 MJ

Average power = 0.69MJ / 9.5s = ~73kW

 

I believe the Prime's listed motor output is from M/G 1 & 2 working together, which the hybrid can't do without the transaxle clutch. M/G 1 in past models was rated around half that of 2.

 

The G5 plug-in no longer has that clutch - it's entirely relying on MG2 for EV propulsion.

I agree I'd have to check more carefully for the G4.

I posted a load of numbers here. I'm pretty confident the 120kW is just for MG2, as stated there. I also say there that the G4 has MG2 = 53kW, and total EV = 68kW, and I mostly trust myself.

 

Is MG2 a physically different motor between the models, or the same one , but 'detuned' by the hybrid's lower electricity supply?

 

As I said in the other post I just linked above with an edit, it's not clear. It has the same model designation, according to NCF, and it's the same physical size in the diagrams. And 650V vs 600V isn't enough to account for the difference alone.

Maybe the current limit in the plug-in's inverter has been lifted too, and that's the "motor" difference.

IIRC, it's not a separate orderable part in the parts database, so you can't check that way.