Filed under: EV/Plug-in, Hybrid, Toyota
Toyota's Irv Miller jumps into Series-Parallel debate again! Now with new definitions!
Over at the Toyota Open Road Blog, Communications VP Irv Miller has chimed in again on the whole parallel vs series hybrid debate, this time with some fresh definitions. The previous postings have generated quite a bit of commentary both for and against Toyota's position. Miller first refutes some previous claims about a ten-mile range for Volt prototypes. Some commenters had attributed this to Toyota when in fact it originated with a Bloomberg story last summer.He also discusses the issue of using nickel metal hydride batteries in a vehicle like Volt. He comes to GM's defense here by explaining that although a NiMH pack could achieve a twenty-mile range from the same sized pack, it would require deep discharge of the pack. This deep discharge would have a serious impact on the lifespan of the battery so that it would not last anywhere near the life of the car.
Perhaps Miller's most interesting, if dubious, point comes when he tries to redefine some hybrid terminology. The series hybrid is simple: it refers to a battery-powered vehicle with some kind of range extender. Miller defines a parallel hybrid as a system like the Honda IMA that does not have an EV-only mode. Most other people in the industry would call this a mild parallel hybrid, since both the internal combustion and electric motors provide torque to the wheels. In function this is little different from the GM belt-alternator-starter hybrid system.
Referring to Toyota's own Hybrid-Synergy-Drive system, he now terms to this as a series/parallel hybrid system. The series portion comes in because the system can drive the vehicle from the electric motor only, in addition to using the combination of the ICE/motor or just ICE. Ford, GM and everyone else using such a system just call this a strong parallel hybrid. This move of changing the terms of the discussion really comes off more as obfuscation of the argument than advancement. It seems like Toyota may be regretting opening this can of worms in the first place. At least Miller does acknowledge that their is no one right answer and that their is room for multiple solutions for different applications.
[Source: Toyota]
Reader Comments (Page 1 of 2)
Tim 12:29PM (9/24/2007)
I just LOVE to see Toyota squirm! They know that distributed renewable electricity is the ONLY long-term solution. Everything else is just treating the symptoms instead of providing a cure. ICE’s with limited “electric assist” like the Prius "synergy-drive" were the first step in electrification. Full electric BEVs with ICE or H2 “range extenders” like the Volt are the next. These range extenders will become obsolete once “fast-charge” batteries can be economically produced. This will take Market Demand, R&D, Scale and Time. Toyota’s 10 year old tech has simply been eclipsed. That’s progress.
By the way, not all “environmentalists” have a benign agenda.
Video: Environ-Mentalism: A New Religion for a New Age http://peswiki.com/index.php/Video:Environ-Mentalism:_A_New_Religion_for_a_New_Age
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AES 1:02PM (9/24/2007)
My comment on Toyota's blog will probably get censored (they do that a LOT) but here it is for the record:
" Irv said: "Just for the record, here, we have no idea what’s going on inside General Motors, and further, have nothing to gain by downplaying their successes, and their advances, with hybrid technology. In point of fact, we wish them the best, because we believe that everybody benefits from hybrids, and from hybrid research and technology."
It's crucial that GM succeed for a number of reasons. First, it's made a sincere effort to correct its image and role in the green car scene, and it has some superior technology to contribute.
Secondly, if foreign automakers achieve even greater success than they already have - mostly due to outdated reputations about reliability and economy, as well as trouble with unions - there are going to be disasterous long term results for the American economy. Toyota may have many jobs in America - Irv's being one of them - but ultimately the flow of most of the cash is going OUT of the country and into banks on foreign soil.
Don't get me wrong, you shouldn't buy a lemon to save America, but if it were down to a plug-in Prius vs. a GM Volt, there's more to consider than just MPG numbers.
As for the whole technology debate: conveniently redefining the Prius as "series/hybrid" doesn't really help much. If the plug-in HSD engine has to cope with driving the wheels as well as recharging a larger generator, it's become a jack of all trades, and a master of none. It'll have to deal with a lot of dynamic load changes no matter what the situation.
re:deep cycling -> Irv, you're blowing smoke. Deep cycling is a familiar problem to anyone with EV experience, and upgrading a car's battery pack in size doesn't alter the problem - or its solutions - one iota. If anything, making the pack larger actually makes the solution somewhat easier, since there are fewer constant cycles that risk depleting the battery. The Prius doesn't let its tiny pack even get below 80% SOC, because it gets cycled for constant small loads that are proportionally large to the pack size.
re:"hotel loads" - as with houses and hotels themselves, this is a problem that is far better addressed with intelligent insulation and design, rather than the appliance itself. ALL cars' mpg ratings are made under ideal conditions without unnecessary loads - Prius included! Taking aim at any car's all-electric range with "hotel loads" is really a bit of a cheap shot, and a hypocritical one at that."
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GoodCheer 1:29PM (9/24/2007)
I can't help but feel that calling a parallel system a "Series-Parallel" Hybrid is very much akin to calling a series system a "BEV with a Range Extender".
Once again, we should all be cautious not to let marketing managers tell us what things are.
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Snowdog 1:33PM (9/24/2007)
The should censor ignoramuses.
I'm with Irv on this one. I don't see it as a cheap shot to mention that when driving slow, accessories can actually draw more power than the motor and that will significantly alter mileage. Facts are not cheap shots.
He is absolutely correct that deep cycling the batteries kicks the crap out of them. The Prius never deep cycles and taxi companies have put 400 000kms on a battery back and it was still going strong. As you note they do this by keeping a very high state of charge. If you are running a PHEV in pure electric mode for 40 miles you are deep cycling and that will kill most batteries quick, including the Nimh that Irv was talking about.
This is why it relatively easy to built a HEV, but quite difficult to build a PHEV, PHEVs are hell on batteries.
The toyota is a series/parallel hybrid, it has two electric motor/generators so it can use the gas engine to generate electricity and drive the car with an electic motor at the same time, just like series hybrid.
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AES 2:09PM (9/24/2007)
Counterpoint to Snowdog-
"I don't see it as a cheap shot to mention that when driving slow, accessories can actually draw more power than the motor and that will significantly alter mileage. Facts are not cheap shots."
The toll that accessories take will be the same regardless of what format the PHEV is - series, parallel, whichever. So it's an equal playing field, and GM has always acknowledged that the optimum electric range is achieved without the AC on.
"Irv is absolutely correct that deep cycling the batteries kicks the crap out of them."
This is one of the reasons why the EV1 was impractical for widespread use. However, the deep-cycling issues are solved by providing a bigger, more energy dense, more mature battery, and only discharging it 50-70%. Even at brutal 100% drain, many modern li-ion cells can withstand up to 3000 cycles. This is why GM is so bullish on li-ion technology, and is seeking to capitalize by being the first to embrace it. Don't be surprised if the eventual volt pack lasts over 200,000 miles.
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philmcneal 2:18PM (9/24/2007)
his explanation of "hotel load" is interesting, he certainly has the inside info on what to expect from Toyota them selfs. I just hope its at least 20 km no accessories and I'll be a happy man, I'm sure they can optimize the electric mode for longer trips but mpg will be considerably high, hopefully in the 100+ mpg range if they tweak the prius some more, but without making it slower as well -_-;
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AES 2:24PM (9/24/2007)
"If you are running a PHEV in pure electric mode for 40 miles you are deep cycling and that will kill most batteries quick, including the Nimh that Irv was talking about."
WRONG. The plan for the Volt is to discharge the battery by 8kWh (50%DOD), then start recharging it. And 8kWh is more than enough to go 40 miles.
Snowdog, you are reiterating a very common misunderstanding about PHEV design.
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Snowdog 3:07PM (9/24/2007)
As far as accessory load. It is a level playing field when Toyota fields a PHEV (and quotes accessory off numbers for the electric range), right now there is no real electric range on the toyota to take a beating.
As for the 8KWH is plenty for 40 miles, you need to back that up. So far you are talking about a car that doesn't exist. You don't know the mass, you don't know the aerodynamics's, you don't know the conversion losses from chemical -to-electrical to mechanical energy to deliver it. When you have hard numbers on the Vapor vehicle, let me know.
Almost no lithiums survive 3000 deep cycles. Mainly A123 claims to, but only if you limit the current draw, draw current quickly and they life cycles drop to about 1000.
I am very happy to see GM build a first of it's kind pure serial hybrid, but the Toyota guy said nothing out of line that deserved the first troll bait post against him.
I find it refreshing that we can get interaction with car execs on their blogs, it should be used as a chance to ask actual interesting questions or make useful suggestions about products. Posting flame bait there isn't helpful in any way.
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AES 4:16PM (9/24/2007)
Snowdog-
"As for the 8KWH is plenty for 40 miles, you need to back that up"
40 miles in 8kWh is about 5miles/kWh, or 5mpk.
For comparison to real life EVs:
The EV1 got OVER 5mpk with a mass similar to what the Volt is planned for (~3000 pounds)
The Rav4 EV got 4.25mpk despite being an SUV having over 1000 pounds of batteries.
The tZero got 5.88mpk.
The Hymotion Prius gets over 8mpk!
So ~5mpk is a perfectly reasonable efficiency based on real life experience.
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GoodCheer 4:18PM (9/24/2007)
SnowDog: "As for the 8KWH is plenty for 40 miles, you need to back that up."
The numbers AES provides for the Volt range vs. energy use are pretty much in line with most electric vehicle drive systems: It is generally safe to assume you'll need about 200-300 Wh/mi, so assuming 40 miles on 8kWh is on the optimistic side of that range (8000/40 = 200).
This is corroborated by the data provided for the Tesla Roadster, 52 kWh with a ~225 m range (230 Wh/mi. This is also what the EV1 was getting ~120 miles on 26.4kWh (220 Wh/mi). The three cars are similar enough in size that I consider the Volt's claims quite reasonable.
While it's certainly true that we don't know the exact conversion losses and total drive efficiency, I think we have a pretty good guess based on previous experiences.
AES: "If the plug-in HSD engine has to cope with driving the wheels as well as recharging a larger generator, it's become a jack of all trades, and a master of none. It'll have to deal with a lot of dynamic load changes no matter what the situation."
I really don't think that will be a problem. Since the torque delivered by each of the electric motor will be totally controlled by computer, there should be no problem in smoothing out dynamic loading.
As others have said, accessory loads can be a significant fraction of total load in your car. I know I can feel it in my speed when my AC compressor kicks on on the highway. The torque of the generator could be made to fade on and off much more smoothly than that.
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GoodCheer 4:20PM (9/24/2007)
SnowDog: "As for the 8KWH is plenty for 40 miles, you need to back that up."
The numbers AES provides for the Volt range vs. energy use are pretty much in line with most electric vehicle drive systems: It is generally safe to assume you'll need about 200-300 Wh/mi, so assuming 40 miles on 8kWh is on the optimistic side of that range (8000/40 = 200).
This is corroborated by the data provided for the Tesla Roadster, 52 kWh with a ~225 m range (230 Wh/mi. This is also what the EV1 was getting ~120 miles on 26.4kWh (220 Wh/mi). The three cars are similar enough in size that I consider the Volt's claims quite reasonable.
While it's certainly true that we don't know the exact conversion losses and total drive efficiency, I think we have a pretty good guess based on previous experiences.
AES: "If the plug-in HSD engine has to cope with driving the wheels as well as recharging a larger generator, it's become a jack of all trades, and a master of none. It'll have to deal with a lot of dynamic load changes no matter what the situation."
I really don't think that will be a problem. Since the torque delivered by each of the electric motor will be totally controlled by computer, there should be no problem in smoothing out dynamic loading.
As others have said, accessory loads can be a significant fraction of total load in your car. I know I can feel it in my speed when my AC compressor kicks on on the highway. The torque of the generator could be made to fade on and off much more smoothly than that.
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why not the LS2LS7? 6:18PM (9/24/2007)
I have a fair amount of experience with LIon batteries where I work. I have to say "deep cycling" isn't really an issue.
The things that wear the batteries are:
temperature extremes
high-current discharging
high-current charging
You can deep cycle a LIon at a fair rate 300 times and it'll get a certain amount of wear. You can instead take it down to 90% 3,000 times and it'll get about the same amount of wear if you keep the charge/discharge rates the same. And both situations will also yield as much power out of the battery (and in) as each other (roughly).
The real issue is rate of discharge and charge. See, it's not necessarily, but if you cut the battery size in half in a car and leave everything else the same, you not only cut the battery life (meaning until discharged) in half, but you also double the effective discharge rate, since you're drawing the same amount of power from half as many cells. Each is discharging twice as fast.
This is the concern, if you can't oversize your battery pack, you will have high rate discharge. This will increase the strain on the pack and the rate at which the pack wears out. It'll do so, even if you only discharge the battery 20%, because it's not the depth to which you discharge that is the issue, it's the rate at which you do it while you are doing it.
However, there's no evidence right now that GM is making an error in this department. Toyota hints at it, but we'll just have to see.
There does seem to be a big dose of sour grapes in these statements. We all know the ICE in the car can kick on to cover any deficit due to hotel loads. So what Toyota is really saying is that the Volt isn't really a plug-in. But Toyota isn't saying "but ours is", they're just saying that if you can't have a 40 mile plug-in, why have one at all?
Even if I get a 20 mile plug-in, it could halve my fuel use. Cut it to near zero if I can get work to put in plugs for me to plug into.
Toyota should stop whining and see what happens. Maybe plug-ins will be a bust, maybe not. Why not let GM find out for them?
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rgseidl 9:17PM (9/24/2007)
Fear - Uncertainty/Confusion - Doubt.
Toyota's system has always been classified as a single-mode compound hybrid, with part of the engine power transmitted mechanically and the rest via the less efficient electric path. The fraction depends on the speed, because of the CVT functionality inherent in a planetary gear set with two speed inputs. There is no need for a separate transmission, but at a certain speed, one of the electric machines has to be kept stationary by electromagnetic forces. This requires high torque ratings for both electric machines, adding a lot of cost.
Avoiding this inefficient point is the objective of the upcoming GM/Daimler/BMW two-mode hybrid, which reconfigures the CVT to save fuel even at freeway speeds. The electric motors can be smaller and also eliminate the torque converter. Even so, the system is more expensive to produce than the single-mode type.
In a purely parallel hybrid, you use a regular, purely mechanical transmission. Typically, one with discrete gears is chosen, making this the cheapest available hybrid architecture. The single electric machine can be rated at any power level and be fitted on either the engine or the transmission side of the clutch or torque converter.
The cost of the battery comes on top of the electric machines, power converter and mechanical transmission components discussed above.
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Snowdog 9:25PM (9/24/2007)
Thanks for the info on WattHour/mile. I still think the battery is the challenging part. Lithiums have a nasty habit of dying even when not used.
I still think the Toyota article was pretty tame, he was primarily talking about limitations with NiMh.
It will be interesting to see how GM delivers a 16KWh A123 pack in sub 30K car.
Though for me it would be a waste, I don't have a place to plug in a PHEV. GM should make a s small battery HEV version for those without a place to charge it. It could be MUCH cheaper when you remove about $10k worth of batteries.
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AES 5:11AM (9/25/2007)
"GM should make a s small battery HEV version for those without a place to charge it."
Far as anyone knows, that's the plan for the plug-in Vue Green Line. GM isn't putting its PHEV eggs in one basket. I still think they should consider non-SUV's though (Aura, Astra, etc).
"if you can't oversize your battery pack, you will have high rate discharge. This will increase the strain on the pack and the rate at which the pack wears out"
Another excellent reason why Irv's original blog about smaller battery size being an advantage was complete bogus.
Overall, the second blog entry has a much more conciliatory tone than the first, if not completely contradictory to the first.
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T2 8:47AM (9/25/2007)
Snowdog, I have been suscribing to the batteryless hybrid for quite some time. I proposed a bidirectional inverter that connects the two busses, the HV rail and the 12v, using a two winding high freq ferrite transformer for galvanic isolation. About 900W should be enough to start the engine or allow reverse and short distances with forward speeds up to 8mph with the engine stationary. I refer to it as the "Virtual Battery" technique.
A normal size lead acid battery (72AHr) could theoretically supply the car for an hour in a series hybrid design for that described duty. Or perhaps 40mins in a Prius which has comparitively huge mechanical losses around 28%. What to do with the energy from regenerative braking ? Well, this could be safely dissipated in a dynamic braking resistor built to absorb 50kw for 10secs. With the Prius for instance the NiMH battery is only allowed to absorb (scan tool measured) around 50A (10kw) for battery longevity. At 50mph Prius KE is 540MJ so complete recapture would take 54secs LOL. Pity the drivers behind you !
That's why IMO regen is so overated um... well it certainly is at that 10kw level. However I believe regen is important for reducing brake wear (photographs from one particular owner showing state of the pads after 80k miles are impressive) and allow the use of cheaper less durable disc brakes for those infrequent emergency situations.
One more thing you like the 28Hp from the battery providing 'assist' ? Think again the Prius engine doesn't do its duty and reach full power of 76Hp until late in the game at 51mph You heard right, at 20mph it makes only 55.4Hp. Constrained by the PSD equation MG1 = 3.6 ICE - 2.6MG2.
Try this :
Plug in the max for MG1=10,000 rpm thus allowing ICE rpm to be big for a max acceleration rampup.
Now given that MG2 is fixed geared to the wheels such that MG2 = 6000rpm at 100mph.
[The following refers to the Prius internals with pedal to the metal acceleration ONLY.]
With all this info you should be able to do these.
The Quiz for Irv Miller
Question #1 How much engine power at 20mph ?
Find MG2 then Compute ICE rpm from equation using MG1=10000rpm.
Then ICE rpm/5000 times 76HP = engine power.
that previous line is valid because the 1NZ-FXE engine is pretty much constant torque.
Question #2 When MG1=10000rpm, ICE =5000rpm what is road speed ?
Hopefully evaluating the above expressions will give anyone some insight into the shortcomings of the Toyota HSD and why it is in the shadow of the series hybrid being pushed by GM. Their engine can reach full speed at anytime and in the traction department of the VOLT there need be but just one gear mesh in the whole shebang ! Too bad they broke with Fiat because that 105hp Panda Aria 2 cyl turbo engine would fit in perfect here in my version of the VOLT.
What puts me off a Prius purchase is the analysis above and then the absolute complexity of the electromechanical system despite the elegant simplicity of the HSD - that is the enigma of the Prius.
In practice skilled Toyota mechanics are apt to swap out whole transaxles rather than try to change MG2, say, involving huge expense to the owner. Preferable to the risks of even larger labor charges if an MG2 swapout didn't cure the problem since the whole engine/transaxle assy has to be removed from the engine bay for rework each time. That would be another advantage of the VOLT if you can change the traction motor without needing to pull the whole engine from the car. I'll agree it's not a problem now but when 80,000 miles are reached by 300,000 Prius we shall see.
T2
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Snowdog 10:32AM (9/25/2007)
I have no idea WTF you are rambling on about. A battery less hybrid, and you want to use the 12v lead acid to store power for hybrid operation?
Kiss your battery goodbye in short order. Lead acids don't respond well to deep cycling at all. Not to mention that you don't even have 1KWh of juice even if you flatline the battery.
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TMS USA 10:37AM (9/25/2007)
To AES - Actually, we do not censor comments to our Open Road Blog (http://blogs.toyota.com/), save for those that are clearly inappropriate because they contain obscenities and the like, a violation of our publishing standards.
We welcome opposing viewpoints and think the debate re this subject and others of high interest in our business is healthy. Makes a more entertaining and informative read for most Toyota Open Road Blog readers.
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T2 1:52PM (9/25/2007)
snowdog, I expect better from you. Unfortunately I can only make you more informed. I can explain things for you snowdog but I can't understand them for you. You have to do some spadework also.
"Not to mention that you don't even have 1KWh of juice even if you flatline the battery."
Well the Prius NiMH only holds 1.3KWHr for that matter which several people online will be only to ready to affirm.
The prismatic cells are rated 6.5AHr and there are 202 volts of them. So 202 times 6.5 = 1300WHrs or 1.3KWhr. OK !!!
My lead acid is 72 times 14v or 920WHr or 0.92KWhr. The ENERGY performance of the two available chemistries or how many miles you can get with them as you can see are not wildly dissimilar.
So why then does NiMH cost $2k+ ? Well, in the Prius this battery can come at you at 21KW (28Hp) continuously. Whereas lead-acid could be cranked at 700amp with a 9v terminal voltage yielding only 3.6KW and then only for a few seconds at a time or you will kill it, of that I am sure you are aware. That is a huge disparity in POWER capability.
So the lead-acid will get you 3/4 the distance just not at 42mph but 8 mph may be possible without damage to the battery plates. 900w (1.25Hp) can be 250lbs draw bar pull at 2mph dropping to 65lbf at 8 mph I am assuming flat ground and no A/C of course nor 200W stereo.
Perhaps snowdog could give me an example of your great learning : Define horsepower for us in ft-lbs/sec ?
The mistake people make with the Prius is thinking that it is an electric car. So.....
A PRIUS IS NOT AN ELECTRIC CAR AND WAS NEVER MEANT TO BE.
This explains why Toyota appears reluctant to have their design hi-jacked into a battery electric vehicle or PHEV. Perhaps in 2050 when gasoline is $100/litre but not now.
The Prius is all about being an ELECTRIC TRANSMISSION to map the internal combustion engine to the torque and speed demands of the road maintaining the fuel economy high by keeping unnecessary engine movement to the minimum.
As a byproduct they are able to offer limited electrical operation. But some people, SOME PEOPLE want to turn this vehicle into an electric toy. LOL
The electric transmission is vastly superior to a mechanical CVT. I am not clear on what feedback and computer controlled elements dictate the internals of a mechanical CVT but the Prius knows precisely what its system is doing via the stator current in MG1. Simply put, 100 amps scales to 82lbs-ft from the engine exactly and is immune to large changes in temperature. On the contrary with CVT mechanisms however, lubrication and critical physical dimensions will be greatly effected by expansion /contractions with temperature. Heck they are even sensitive to the wrong CVT lube oil type. I would bet there aren't too many CVT cars in Anchorage.
Generally there are those of us who would be quite happy with the Prius without the NiMH. It gives a headache in that this chemistry slowly self discharges over a few days, some packs hold up better than others. The reason Toyota installs a lead-acid battery on board is to reliably maintain computer clocks and security alarms etc. Unfortunately Toyota has made it a royal pain to get in and recharge when it goes down which doesn't help matters either. It would just help peace of mind and resale value not to have an aging device as part of the traction system which has the ability to become an unexpected showstopper but that's a problem for me, despite 300,000 owners who obviously disagree with this mantra.
T2
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Snowdog 9:58PM (9/25/2007)
Even at full SOC, the lead acid is under 13V.
You also haven't addressed the the lifespan factor, if you start using a lead acid battery as drive motor, you are going to destroy it in short order and likely find yourself stranded your first winter.
Lead Acid is just about the worse battery chemistry to use for an electric drive.
Using the motor-genset as a transmission is interesting. Though so far the only delivered Hybrid that intested me was the the Insight as I like to drive manual and it was very purpose built and had the best gas mileage by far.
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