More on Regeneration in EV mode

Any idea how much charging the packs need before it will run from them again, perhaps allowing regen? Like could you stop at the top of a mountain, plug in for 30 seconds, then be able to fill the pack it had started charging?

 

Two things here: I have to imagine there's a damn good reason it's designed this way, otherwise why would they overcomplicate it? It's almost certainly got something to do with battery life.

And given my complete inability to fully charge the single hv battery in my III with regen, unless you literally live on top of a mountain, how is this even an issue?

 

With some of the bright minds here on PC, I'll predict that when the PHEV finally makes it to market, the bright minds will take no time at all, figuring how to bypass that function, as part of a process of adding more battery packs, to extend range. Not that THIS PC member would ever do such a thing.

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I live on a mountain, above 6000'. As I'm about 5000' above the valley below, regen will be a key part of any PHEV purchasing decision for me.

 

on the video for the plug-in hybrid, it says that the (2) seperate packs will re-charge with regular driving assuming they are not completely depleted right ? Once they are, they can only be charged via plug ?

 

Yes. With initial start-up in EV mode, the battery packs will regen while EV mode is still active. Once the EV mode is fully depleted, the packs are disconnected and won't be able to be regen'd from that point on. The car goes into HV mode, and runs like a regular Prius at that point. So from that moment on, the regen will only recapture on the HV battery pack.

Once you stop and charge the plug-in battery, that is when EV mode will be able to be used again.

 

We must be neighbors. Full regen would be great. It will take just about the full EV charge to get from home to one of the surrounding mountain passes. Being able to fully regen on the decent would be great - another 12 miles for free.

 

LakePrius, I'm a few hundred miles to the south of you, but at a comparable elevation.

I hope Toyota decides to keep the EV mode button on the PHEV instead of removing it as they apparently have for the prototypes. That way, on a longer drive, one could decide when to use the batteries and when to use the ICE, depending on conditions. That would also make it easier to regen into the PHEV batteries when terrain permits.

 

So there is no way to charge all the batteries while in EV mode? I would think that would be really convenient to get the most efficient mileage.

Or am I not understanding this correctly...

 

The way I understand it (and I'm sure someone will correct any errors here) is that the PHEV prototypes have three batteries which participate in propelling the vehicle - the regular traction battery (which has been changes to Li based for more capacity) and two "EV" batteries which each provide about 6 miles of pure EV range.

Only one of the two EV batteries is connected to the circuit at a time. While connected, it can be charged via regen just like the regular traction battery. However, once the charge in the EV battery is depleted, it is disconnected from the car's circuit. Once disconnected, it can only then be recharged once the Prius is plugged in.

When the first EV battery is disconnected from the circuit, the second one is connected. It stays connected to the circuit until it too is depleted, then it is disconnected and you are left with a regular old Prius - albeit with a better traction battery.

So the overall increase in mileage is partly from the better traction battery and partly from the two EV batteries.

 

This is stupid on Toyota's part and bad engineering. They should leave all 3 batteries in-circuit together (parallel). This way the I2R losses in the pack are cut in thirds. This would also give you more hybrid capacity even if you never plug in, which wouldn't hurt and only improve the recovery especially for those that live in hilly terrain.

I suspect that they are doing things this way so they can re-use as many components as possible without any re-engineering. Keep the same pack and BMS, just switch them in/out. Non-optimal from an engineering standpoint, but no extensive (read: expensive) re-engineering needed as the existing designs are already proven.

I would never buy such a vehicle, especially after seeing what my Prius is capable of as a plug-in when done right, or at least better than how Toyota wants to pull it off. (See my PHEV thread for more information.)

If I had Toyota's Engineering team, I would install one larger pack, even if based on the same NiMh chemistry, and upgrade the DC-DC boost converter to allow full EV acceleration (MG2's limits). Right now, at least in the Gen II, we are limited to ~20kw by the boost converter, period. The challenges to hack this as an individual are almost prohibitive, as it hits up against a requirement to alter software in the HV ECU which we do not have access to. For Toyota/Denso this is a pretty easy enhancement however, as proven by them doubling the boost converter in the prototype PHEV's.

I can accept full regen in my entire upgraded pack, (I don't have the original pack anymore) so if I had a big enough hill, I could start off almost dead at the top and recover over 6kw down the hill, and that would be enough to power me up the next hill if it was slightly smaller. Right now I have manual control of how much electric assist and regen the car uses, so I can perform terrain anticipation. I doubt seriously Toyota will ever allow manual control of anything like this, but it shouldn't be all that hard to work with the Nav manufacturers to have it spit out upcoming terrain data when you pre-plan your route. This will drastically improve mileage in the hills when you have a larger pack!

 

That is a really silly set up, just as you pointed out pEEf. I don't see the purpose in keeping them separate. It could be just as easily done in a similar fashion with one big battery and a computer system forcing you out of EV mode if the battery runs low, perhaps with a smaller EV "emergency" battery. I'd be more into that.

I like the idea of a plug-in Hybrid but there would have to be a way bigger incentive than 15 miles of driving charge with no acceleration for me to bother plugging it in.

 

I got on Techstream and you can download the schematics and service manual for the PHEV now. It does indeed have 3 packs with 3 separate battery ECU's. The Charger looks like it's under the passenger seat:



They list the battery as 345.6v @ 5ah. The charger is rated at 2kw when running on 240v and derated to 1kw when running on 120v. The documentation claims it will take 180 minutes at 120v and 100 minutes at 240v to charge the packs to 80% SOC. You cannot charge the packs to over 80% SOC while plugged in, the charger will stop.

They state that EV mode will work up to 62mph, but will only run for 18 miles before starting the ICE regardless of SOC. It will also start the ICE if you ask for heat. Why they didn't make the A/C system work as a heat pump is a mystery.

Here's the pack:


Here's one cell:



There are even 3 separate service plugs:

 

Nice post. From the diagrams, it sure doesn't look like there is a space/packaging issue that is being solved by using three packs instead of one.

 

I agree, I don't see any particular benefit to having it set up that way unless there is some kind of safety issue I am not aware of. Most likely it is more expensive to make it it the other way.

Actually I think saving money on their end is the most likely culprit due to the cost of lithium ion batteries - such as how the Chevy Volt costs almost 50 grand.

 

Or maybe they don't expect as many batteries to make it through the warranty period and having them divided into three like this will make it easier to swap just the one, rather than replace the entire 'pack' at much greater expense?