Filed under: EV/Plug-in, Hybrid, GM, Toyota
Toyota's Irv Miller on Series vs Parallel hybrids
We reported last week on a presentation given by Toyota Executive Vice President Kazuo Okamoto in Japan. One of the slides in that presentation compared series and parallel hybrids and talked about the superiority of parallel as manifested in Toyota's Hybrid Synergy drive. Toyota wasn't able to provide ABG with a text of the presentation, but Irv Miller, the Group VP for Communications at Toyota here in the States, has elaborated over on Toyota's Open Road blog.
First of all he reiterates the mantra that GM has been repeating all year of energy diversity. In the future there are likely to be many different fuels and energy sources in use for transportation. He goes on to explain that the size of battery that would be needed for a useful series hybrid would take to long to charge and be too large and heavy to make it perform better than a parallel hybrid. He also mentions that said batteries haven't even been fully developed yet.
Mr. Miller and Toyota may well turn out to be correct in their assessments of series hybrids in the long run. However, there was plenty of skepticism about the work that Toyota did on parallel hybrids over a decade ago and if they hadn't proceeded anyway we probably wouldn't be where we are today. No one has abandoned parallel hybrid development in favor of series. They and other technologies are continuing on parallel paths. Ultimately we may well end up using all or none of these. But for now let's see where they go. Thanks to Irv Miller for chiming in.
[Source: Toyota]
Reader Comments (Page 1 of 1)
why not the LS2LS7? 7:20PM (9/10/2007)
That's a good slide showing the tradeoffs. The generator and motor have to be bigger on a series hybrid (no reason for the battery to be bigger though, unlike what this slide shows). Bigger means more weight, more cost.
But honestly, if you want to run on electricity only (a plug-in with an all-electric mode) you have to make the motor large enough to drive the vehicle itself without the ICE assist.
So I'm interested in seeing how Toyota is going to avoid doing a largely series plug-in hybrid. Basically, if plug-ins catch on, they'll be caught with their pants down, at least for a while.
It's nothing they can't survive, they're reasonably nimble.
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scappy 8:50PM (9/10/2007)
Agreed the large motor of the series hybrid lends itself to perform much better in an all electric mode. Additionally 95% of people will be charging their cars over night, so the manufacturers are probably aiming at a 6 hour recharge time. Which yes is long, but time flies while you're sleeping. Secondly Toyota is probably refering to old reliable NiMH batteries and leaving "risky" li-ion out of the equation.
This is pretty much a PR spin exercise.
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Benson Leung 8:52PM (9/10/2007)
I think this fellow makes a compelling point. The series hybrid has a lot of promise, and would be a big step in the direction toward full battery electric vehicles, but much of the hype about the Volt and other series hybrids are theoretical. The batteries remain to be developed.
Another point he makes is that supporting the HSD is not a bet that will cost Toyota if the plug in hybrid becomes successful...
To answer your question, LS2/LS7, if plug in technology catches on, Toyota will be able to avoid having to develop a series hybrid because they can simply augment the "full" HSD with more advanced, higher capacity batteries and/or bigger drive motors... two components that will necessarily go into a series hybrid as well. Toyota has sold over a million "full" hybrids in the past decade, so the PSD technology integral in the hybrid is quite mature, and will have economies of scale on its side.
HSD hybrids are available today, and what Toyota is reiterating is that even if plug-ins get big, HSD won't be made obsolete... HSD can be upgraded with bigger batteries and bigger motors, the very same that are necessary for a series hybrid like the Volt.
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GreyFlcn 3:01AM (9/11/2007)
What do you mean the batteries remain to be developed?
A123 Systems and AltairNano have been sporting their lithium polymer batteries for quite some time.
The series hybrid though will be quite desirable.
Since I can defiantly see people wanting the extra flexibility and range. And just in general, the security.
For instance most car drivers carry a spare tire, even though they might not even use it for years on end.
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AES 5:52AM (9/11/2007)
Toyota is playing a dangerous PR game because it is championing its parallel hybrid approach while simultaneously developing plug-in hybrid capability. However, for those of with a modicum of technical knowledge, Irv's BS is hot and steamingly obvious.
If you're going to build a PHEV, the entire premise is that the car will be more electrically dominant than a standard hybrid. That means adding a larger battery to provide more EV-only range as well as more EV assistance during hybrid operation. However, a smaller battery pack will be subject to more charge/discharge cycles on a more frequent basis, and thus a shorter lifespan than a larger pack. If Toyota's engineers have any sense they'll know that deep-cycling (draining the pack dry) will be extremely bad for the pack's lifespan. Thus, I suspect that for their prototypes they will have the internal combustion engine kick in *much* earlier than a series hybrid would, thus preventing deep cycling. However, even during normal hybrid driving the smaller battery would still be subject to a *much* higher workload than the standard prius, and the more you use the ICE to compensate for this, the more you defeat the entire purpose of the PHEV. Moreover, if the electric drivetrain is much more utilized, and the battery is only recharged by regen or plugin - and not by any onboard generation- it's bound to run very low - if not dry - on a long enough trip. And then you're just left with a very expensive standard Prius with sub-standard Prius abilities.
The bottom line is that Toyota is not immune from having to pursue larger, safer, more energy dense batteries for its PHEV's, and it needs to stop fooling itself with regards to this issue.
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Yggdrasilly 11:45AM (9/11/2007)
"It looks like our competitors might beat us to the market with this new technology--quick, let's tell everybody it's unimportant (until we can market it ourselves, that is)"
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Jon 12:41PM (9/11/2007)
GreyFlcn,
That the batteries remain yet to be developed is made clear from the joint news release issued by GM and A123. One can only assume that they have not yet sufficiently optimized existing batteries for use in the Volt.
The press release also states that A123 is one of two vendors GM has contracted with to develop the batteries. GM is confident that one of them will be able to develop the batteries by the projected release date of the Volt in 2010.
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Steve F 9:41PM (9/14/2007)
The real question about Toyota is if what their PR is saying and what their R&D is developing could be different. I may be wrong but Toyota could be developing a serial type hybrid like the GM E-Flex but keeping it secret and would bring it out if market accepts the full plug-ins. Seems I have notice in pass Japan auto suppliers seem to keep thing more secret until closer to release.
As for myself I hope I am wrong and GM can deliver ahead of Toyota and take a technical lead on plug-ins.
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Chris M 3:55AM (9/15/2007)
AES, I can assure you that Toyota engineers are well aware that deep cycling shortens battery life. That is why the Toyota Hybrid Synergy Drive hybrids are designed to keep the "State of Charge" between 85% and 35%, the optimum range for their NiMH batteries and can recharge the batteries from the engine when needed. A plug-in version would follow the same rules, but would use a larger battery pack and a plug-in recharger. A "serial hybrid" should be designed to the same SOC constraints, if long battery life is desired.
Granted, a higher energy density is desireable, but Toyota could bring a PHEV to market soon using existing NiMH batteries, then quickly adapt to newer higher energy density batteries when they are ready and available.
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AES 4:32AM (9/15/2007)
Yes, but the weight of the NiMH cells needed to give a range of 7-8 miles (which is what their prototypes are currently capable of) would rival the lithium ion pack in weight, and be a significant underperformer by comparison. Plus take up all cargo space. In other words, the slide showing the relative size/weight of the different components is rather not at all to scale, if not downright deceptive.
Consider the following:
Secondary NiMH battery of 2.6 kWh@45wh/kg=58kg+
Regular Prius battery of 39.52kg
Total weight=97.5kg or 215 pounds
Compare that to a Volt pack of 270-320 pounds (the former with next-gen A123 cells@~130wh/kg, the latter with standard M1 cells@~108wh/kg)
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