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]


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