Hymotion Conversion Technical Discussion

its not supposed to change Prius operation, but what i hope to do is force EV mode and not start the car up for my commuting needs. if i have to set CC at 34 mph (if it could be set that is) i will do that.

otherwise, the biggest benefit of plugging in: not burning gas at all, especially for very short trips of say 2-4 miles, would be lost.

i am displaying my Zenn at the Lacey Alternative Fuel Fair this Saturday and i be willing to bet that someone will have the Hymotion mod installed with someone to talk to.

cant guarantee it, but i be willing to bet on it. i have seen several of their test vehicles (most Ford Escapes to be honest with ya) running around here so would be hard to believe they will not have a showing there

 

C) I think with EV mod and slow to moderate acceleration you can run "pure EV" as long as there is energy in L5 ?!

D) Maybe we should measure the offset of "very small number of possibly more polluting startups" VS "lots of less polluting startups". I personnaly think that the first will win.

E) My understanding is that as soon as the ICE kicks in, some relays switch the Prius to "ICE + OEM traction battery". Then if you go back to EV the L5 is back as the sole source of electricity. If my assumptions are rights, then no worry about the efficiency.

 

From what I can tell, Hymotion basically uses the topology described here:
Battery Pack Configurations - EAA-PHEV

Here's a crack at a basic theory of operation (just a guess, based on the above and knowing how some of the other conversions work):

The battery pack is ~5kWh, although its unclear if that is usable or raw capacity (ie net or gross). The 30-40 miles specified is presumed to be high speed / high mpg rather than EV miles based on this capacity. True EV miles should be closer to 15-20. Most other manufacturers would call this a 15 or 20 mile pack, rather than a 30 or 40 mile pack. The general approach seems to be a cross between the Cal-Car's and Manzanita Micro's methods but with the nice upgrade of a Li-ion pack and BMS. Like the Cal-Cars (latest gen) they appear to use an SOC spoofing controller, probably all part of their Li-ion BMS. This controller reports idealized SOC values (probably CCL/CDL values as well) to the HV controller based on driving conditions rather than actual battery SOC. The ideal value depends on a number of factors including temperatures, and operating mode (EV, high speed, regen etc). In general it probably ranges from ~60-74%. By 80% the HV controller starts burning power in inefficient ways to get the SOC down ASAP. In addition the controller is responsible for maintaining the SOC of the oem pack (probably at ~60%) and monitoring the secondary pack to decide when to revert back to basic HEV mode to protect the PHEV pack. Like the Manzanita Micro method, the secondary pack is connected through a unidirectional dc:dc converter rather than the simple contactor used by Cal-Cars. This has the advantage of keeping the output voltage ideal to a lower DOD, and makes the secondary pack voltage an independent variable. The disadvantage is that unlike the simpler Cal-Cars method, or the more complicated bidirectional dc:dc converters used by EnergyCS, and Hybrids plus to name a few, regenerated power can not be fed back into the secondary pack once the oem pack is full. Like both the Cal-Cars and Manzanita Micro methods one would expect that the oem pack is never actually disconnected during operation but I'm not positive on that. Doing so creates a lot of complications, and if you were going to solve all those problems you'd probably be better off pitching the whole oem pack as others have done.

All in all it looks to me like a pretty good compromise between complexity and cost.

I think the comments on EV use are pretty accurate. Argonne did find that emissions in a PHEV are higher when EV mode is used. I'm not sure how much higher though. Given that the Prius is considerably lower in emissions than most vehicles I'm not sure this is a big concern, but obviously shouldn't be ignored. In general there are several thoughts on addressing this. One is the high speed EV or forced stealth mode (FSM) being tried by Plug-In Supply Inc of Petaluma California. This basically simulates an out of gas condition (its a bit more complicated than that) and lets you run EV mode under hard acceleration and up to ~52mph (just limited by power avail). This of course has its problems, but is really nice if you have an intermediate speed (~45mph) commute that is shorter than your pack range. If the ICE never starts, you never have to warm it up. People are also looking at block and/or cat heaters run of either the wall outlet or even the PHEV pack. For now I think efusco is pretty right on with his strategy.

Rob

 

That's a lot of good information. I clearly have not thought this through as well as some.

Argonne national labs has a powerpoint set with a fair bit of information on the Hymotion conversion. I saw nothing there to contradict any information above. There's also a full report somewhere, but I can't seem to dredge up the URL.

http://www.transportation.anl.gov/pdfs/HV/393.pdf

A while back I corresponded with Dave Duval, who works for the Fairfax Co Va gov't and has responsibility for their Hymotion conversion Prius. He confirmed that the Hymotion pack typically "clicks off" around 30 miles of mixed driving. So it's a 20 mile pack as described above. The unexpected part of his message was that there's an on-off switch for the pack, on the dash. (For him it was an annoyance as people would switch the pack off and mess up his mileage.) But, you can turn it off if you want, which might or might not be a factor in how you drive it.

My understanding is that you can suppress warmup at startup with the EV switch. But I think that severely limits your ability to do a hard, unplanned ("panic") acceleration if required. Don't now that for sure, that's just based on my Prius' behavior when I start out in EV mode then flip the ICE on. Have not actually tried to floor it straight out of EV to see what would happen.

Nonetheless, my take on it is as suggested above -- if I use the EV switch and just putter around town I should be able to get pure EV miles out of it. If I'm careful. But driven at the standard urban cycle there's no way to get pure EV out of it, and the ICE will run cold and therefore dirty.

Does anyone know for sure whether 34 is the absolute limit of pure EV? I think not -- I think that you're only guaranteed to stay in EV up to 34. I think that, with the right conditions, the car may stay in EV right up to 41. Which is a world of difference in my neighborhood with lots of 35 mph roads.

The only other thing I've thought about is wintertime heat without the ICE. Again, oriented toward low-speed in-town driving. I'm pretty sure that I'm going to have to hard-wire something to the 12V battery to be able to draw enough current for effective heating. But have haven't seen the off-the-shelf solution I'd care to buy.

 

Thats a very good presentation, thanks!

As I understand it, its somewhat arbitrary and is even different between metric and english unit markets. I think the current "hard" limit is 42mph where the ICE starts spinning to keep the MG rpms in check. There is speculation that Toyota has convinced themselves the MG rpm limit can be raised and that the 62mph EV mode on the factory PHEV demonstration vehicles is achieved purely through software. To my knowledge no one has yet tried to reverse engineer the HV controller & code to figure out how to do that. The FSM hack mentioned above is the best available so far. Althought they've done a pretty good job of making that a clean operating condition (no dash lights, codes etc), last I knew you still had to pull over and restart to get the ICE to come on.

Rob

 

I'm finally catching up on this thread, and in fact have been
corresponding with some semi-local folks about helping one guy
with a pluginsupply conversion [I think]. Some of you
contributing to this thread may be the same people, it's hard
to tell. I've also chatted with several other folks who are
taking various different approaches to this, and believe I've
got a fair overview of what's needed. I haven't looked too
closely at the system that are actually helping capture
regen, though.
.
As efusco points out, just having the ability to push only
10 amps into the stock system would be a serious glide-extender
by itself. Work the stock pack up to 75% and then limit what
you draw on glides to 10 amps, and you could go forever until
the PHEV pack flattens or you need more oomph. The real
design hair comes when you want a> more oomph for a longer
time, and/or b> more regen capability. One of the early
approches was simply paralleling in one or more equivalent
Prius packs, and there were observations that the car learned
about the additional capacity and actually used it. That
may have been an early example of the *opposite* of "SOC
drift" before anyone actually knew what that was.
.
At Hybridfest last year we observed some interesting and not
altogether reassuring quirks of the SOC spoofing they were
doing. The MFD responds almost instantly to what it's told
the SOC is, and when both the stock battery ECU and the
Hymotion pack squirted different values onto the CANbus, the
display would actually flicker between two values. I'm
surprised *that* didn't light a few codes by itself.
.
Greg Hansen [?] at EnergyCS was experimenting with fuel
run-out conditions three years ago at Tour de Sol, as a way
to really really keep the engine off. But this did involve
driving around with the check-engine light on, and having
to clear the codes afterward. So this 52-mph "hack" is
likely to confuse a few people unless someone else has
discovered a way to prevent the engine from running without
upsetting the rest of the system.
.
There's no real harm in *spinning* the engine, and remember
that you can get a lot more push out of warp-stealth if the
SOC is high and still not burn any fuel. Maybe *that* is
what people should really go after, rather than "pure EV",
because on anything other than a trivially short drive, even
if you've gone through S1 warmup you should still be able
to go somewhere on very little fuel. This would also help
allay that issue of not turning the transaxle oil pump, since
you'd at least *sometimes* be squirting a little fresh fluid
down the shaft and into the bearings.
.
Inspired by my recent attempt to rescue someone's car, I'm
adding a fuel-pump cutoff and intend to start playing with
it as a means of killing the engine. Just a simple switch
cut into the very convenient lead that runs through the drivers
side kick panel. I've already played with this a little bit
and know what it feels like when the engine starves for gas,
but haven't actually tried to use it as an operational method
of any sort while driving. It will also be a good training
tool to show other people the car's behavior when it runs
out or otherwise loses fuel supply somehow. The sucker bucks
pretty hard on the way down because it's connected to the
inertia of MG1 through a 3:1 speedup.
.
_H*

 

If you look at the EPA Dyno charts, all the city/urban tests involve a lot of starts and stops. The Dyno chart in the Hymotion test looks fairly typical.

 

I don't know about hills, but they do take into account wind resistance.

 

Certainly, if the L5 "fools" the car into thinking the traction battery is at 80%, there shouldn't be any reason (as long as one isn't "lead-footed") one can't keep it in EV mode for any short trips. That's what I'm hoping for. I got about 55.5 mpg on my last tank (9.0 gallons to fill), but after filling up, my wife took several short trips around town and the mileage for the first 7 or 8 miles was only 39.2 mpg. If I can convince my wife to plug-in after each trip across town (round trip to any place in Cheney isn't more than 5 miles), we should be able to get terrific mileage. Of course, some trips would involve significant hills, and it probably can't be kept in EV mode up them.

Dave M. (Dave in CheneyWA)

 

Well Dave that is the reason i think the other plug in Option might be better since it does change the way the Pri operates and creates a forced EV mode, a mode that can be switched on and off, but would keep you in EV mode at much higher speeds (forget what that was...53 mph maybe) and no matter how you drove, more or less. the only thing that would be somewhat inconvenient is that to get out of that mode, you would have to restart the car...

now there is only the smallest amount of info possible on the subject so it remains to be seen how effective it will be... but to be honest with ya, Toyota officially announced today in the main news media that they are officially doing plug ins, so i will no doubt wait and see the official Toyota version

 

Oh well, I already ordered an L5. I suppose I could get my deposit back (less the $75 processing fee), but would only do that if Norm gets his BMS+ board working to his own satisfaction and releases plans for a do it yourself kit using Lithium-ion. Otherwise, I'll get my installation of the L5 done sometime in November or December, assuming shipping date indicated remains active.

Anyway, you already have a Zenn, so have no immediate need for any plug-in hybrid.

Dave M.