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Toyota Continues Open Technical Discussions on PHEV Designs
Sep 25, 2007 (From the CalCars-News archive)
This posting originally appeared at CalCars-News, our newsletter of breaking CalCars and plug-in hybrid news. View the original posting here.
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Irv Miller, Toyota's Group Vice President, Corporate Communications, continues to encourage broad discussions with the communities of PHEV and V2G advocates as well as those interested in automotive engineering. Here Miller's reference to our responses prompted us and others to continue the discussion. Below is Miller's posting and our response.

Toyota Open Road: September 24, 2007 06:56 AM IRV'S SHEET: Hybrid Tech: You Comment, We Respond­2007/­09/­irvs-sheet-hybr.html?cid=83928879

Back on September 8th, I published a quick piece I called "Hybrid Tech: Parallel vs. Series." One of the great things about the blogosphere is that it's a two-way street, a format that invites, if you will, call and response, point and counterpoint.

So it wasn't long until our friends at (or, more formally, California Cars Initiative for Plug-in Hybrids), to respond to my post with some interesting points. If you haven't already done so, you can read them by scrolling down to the comments section of my September 8 post.

While we're pleased that the folks there are willing to engage in this important discussion, our general reaction to those comments is that unlike the Blue Ray-vs-HD/DVD metaphor that some have suggested, we don't see the series-vs-parallel discussion as an either/or sort of thing. We do not believe that only one solution will be adopted, and all others will be abandoned.

Instead, what we expect is a diversity of solutions. That makes this a very exciting time for anyone who is interested in advancing automobile technology. Just as is the case with conventional internal-combustion engines, we expect to see many different approaches and nuances.

In any case, it seems appropriate for me to clarify a few things, so here goes. . .

First of all, it is asserted that existing Nickel Metal Hydride (NiMH) batteries similar to those used so successfully by Toyota's Hybrid Synergy Drive (HSD) system could drive the Chevrolet Volt (a hybrid prototype that was shown at the Detroit Show in January) 20 miles electrically without any change in the Volt's weight or other parameters if they were designed for what's called deep discharge. Currently, with most NiMH batteries, deep discharge is problematic because the deeper the discharge, the shorter the battery life. And obviously longer life is preferable to shorter life.

Anyway, the CalCars comments point out that that 20-mile figure is double the 10-mile EV range that Volt prototypes reportedly will have and importantly, they attribute that range claim to Toyota.

First and foremost, that 10-mile range is not our claim. That was published in a story written by Jeff Green and Alan Ohnsman in on August 3, and published again on That story cited unattributed information from inside General Motors saying that the Volt prototype will have a range of 10 miles. So that range figure appears to be right from the General's mouth.

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.

With that being said, let us be sure that we all are talking with reference to the same set of definitions. Honda's hybrid, for instance, isn't a series hybrid system. It's a parallel hybrid system. Our Hybrid Synergy Drive system isn't a parallel hybrid system. It's a series/parallel hybrid system. The difference is the Honda system doesn't have an EV mode (series), but ours does. Likewise, the Volt doesn't have a traditional powertrain mode (parallel), but ours does.

Now, here's the deal:

Do we favor NiMH technology? Of course we do. Toyota is heavily invested in NiMH battery technology. In fact, we think we've probably produced more hybrids using NiMH batteries than all other manufactures combined.

But because of our deep experience with NiMH technology, we also recognize the limits of these batteries with respect to cost, size, weight, recycling and life under wide state-of-charge swings. That is why we're developing new Lithium Ion technology.

In theory, of course a series hybrid could be developed that pulled a 20- mile range from NiMH batteries. But it would have to be a purpose-built car that depended upon technology that's not applicable to other products. Meanwhile, Toyota's HSD can be applied, and is being applied, across our entire product range.

But there's more that needs to be said about this business of battery-only driving range and forgive me, here, but this will require some engineering talk.

When range is discussed, it's important to also consider more than just the traction load. We also need to consider non-traction electric loads, AKA "hotel loads."

In many, if not most cases, at low speeds, the "hotel load" (and for you non-technoids, "hotel load" basically means the power demand from devices that are necessary or that are demanded by consumers, but that are not part of the powertrain that propels the vehicle), can be higher than the traction load. And as the automobile becomes increasingly electrified (steer by wire, brake by wire, heat pumps, active suspension, etc.), the "hotel load" will require considerably more battery energy.

Toyota thinks that it's important to let our customers know what they can realistically expect to experience in the future. Sure, it's possible for Car A to get a 20-mile electric range when driven at low speed with the air conditioning, lights and stereo turned off. But that obviously is not how the average person drives. When we factor in high-speed driving, use of the air-conditioning system, the audio system and so forth, Car A's actual all-electric range will be quite a bit less than that 20-mile grail.

But what's more important here is that this discussion about the efficiency of one approach over another is, we believe, misplaced. What's important is not the specific efficiency of a battery vs. a transmission. What's important is the overall package, its acceptance by customers and the product's contribution to sustainable mobility.

The market for vehicles in the U.S. is around 17 million cars and trucks a year. In order to make a substantial reduction on our environmental footprint, the automobile industry needs products that can go to market today, be affordable, sell in large volumes, be easily serviceable and be capable of operating within the parameters of standard vehicle warranties. At Toyota, with Hybrid Synergy Drive, that's exactly what we're doing.

[POSTS BY OTHER PEOPLE AT­2007/­09/­irvs-sheet-hybr.html?cid=83928879 ]


We at are encouraged and energized by the continuing dialogue. We agree that everyone benefits by discussions of hybrid research and technology.

We've asked Ron Gremban, our Technology Lead, to respond to some of the technical issues you just raised. (To keep it short, we don't address everything!)

Ron wanted to be sure to start by saying that "since its introduction, I have been in awe of the engineering that went into the '04+ Prius and Toyota's Hybrid Synergy Drive." (And in his Sept 13 response, he attributed the 10-mile Volt prototype range information to Toyota only because we hadn't seen the previous news reports on which the comment was based.) Ron continues:

I agree wholeheartedly that series, parallel, and series/parallel hybrids and PHEVs will co-exist for some time in the marketplace, if not from now on. No single configuration has all the advantages.

Part of Toyota's strong experience with NiMH batteries comes from the deep-discharge 1990s-technology NiMH packs used in Toyota's RAV4 EVs, some of which by now have well over 100,000 miles on them without significant battery degradation. In fact, the Electric Power Research Institute (EPRI)'s prediction that NiMH and Li-ion batteries can both last the life of a PHEV is based on that field data as well as its PHEV-specific laboratory testing. Yes, cycle life of any battery is reduced with deeper discharge. This merely means that the engineering tradeoffs between pack size, depth of discharge, cycle life, power handling capabilities, etc. must be chosen carefully, using both engineering and economic expertise.

"Hotel loads" must be supplied, if not from a battery, from gasoline at the internal combustion engine (ICE)'s same 15-35% efficiency as available to propel the vehicle. Therefore, all the advantages of using grid electricity to propel the vehicle apply equally to using grid electricity to supply hotel loads. Even when this energy provides less EV range in cold or hot weather use, it is still displacing the same amount of gasoline (or more, since electric A/C compressors are far more efficient than engine-driven ones). The one exception is cabin heating, which is normally supplied from ICE waste heat. When it is too cold for an air conditioning heat pump to efficiently heat the cabin, EV purity can be sacrificed (independent of hybrid type) by running the ICE occasionally to build up sufficient waste heat for cabin heating. ICEs produce so much waste heat that mere occasional operation will be quite sufficient.

Plus a final note from Felix Kramer, returning to a less technical perspective: We agree with Irv Miller's description of the attributes of cars that can sell in the millions. But we suggest a way to get there most rapidly, reflecting the urgency of climate crisis and fossil fuel dependency, is by producing (and selling in surprisingly substantial numbers) "good enough to start Version 1.0" PHEVs from which automakers will all learn. Remember the first cellphones: brick-sized and costing in the thousands? We're glad the manufacturers started producing them to continue improving them while scaling up production.

-- Felix Kramer, Founder, The California Cars Initiative 05:45 PM You can also find comments (some of which overlap with ones at Open Road blog, and some of which aren't all that polite!) at­2007/­09/­24/­toyotas-irv-miller-jumps-into-series-parallel-debate-again-now

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