The information you have provided in support of your argument is too good. After reading this, I am better informed and more positive about GM’s e-flex technology.

Thanks

Vishva

A plug-in HSD (prius) system would actually be more of a “compound” hybrid than a true parallel hybrid, given that the ICE can both recharge the battery and drive the wheels. This is good versatility, but the motor’s efficiency will suffer under the load of performing both tasks. It will have to be made larger to handle the peak load, and its efficiency will suffer as a result.

Meanwhile, a series hybrid with battery buffering could be built to an exact size, weight, and power, and take maximum advantage of valve timing, throttle management, and forced induction. Even with the losses of transmitting that electrical power through the generator, batteries, and inverter, it could still be engineered to be as efficient (or more) than a larger ICE running through a complicated and wasteful CVT.

A Toy rep has since gone on record stating that they want the plug-in Prius to have an all-electric range of 30-60 km (18.6- 37.28 miles). In other words, roughly the same performance goal as GM’s E-flex system.

http://www.autobloggreen.com/2007/09/16/video-toyota-has-goal-of-37-miles-electric-only-range-for-prius/

Now this begs two obvious questions:

1) How can you even think about doing this without using lithium ion technology? GM already has dibs on the A123 technology, so Toy must be looking at other possible suppliers to make this claim. Panasonic has obviously failed to deliver safe or powerful Li-Ion thus far.

Regardless, the shift towards larger all-electric range, and thus a larger battery, pretty much invalidates Okamoto’s diagram showing smaller battery size as an advantage to Toyota’s approach. Seems like a case of “say one thing, do another”.

2) If the Prius plug-in is going to be capable of highway speeds running on electricity alone, isn’t it going to need a more powerful electric motor that won’t need ICE assistance at higher speeds and loads, which negates the entire premise of the HSD system?

According to Google.org’s RechargeIt, the PHEV Prius conversions made using A123 lithium ion technology (the same chemistry that’s been contracted for use in the Volt) yields 8.44 miles/kWh in electric-only mode, implying a 21 mile range on 50% DOD of its 5kWh battery pack. These are the conversions that Toy strongly disapproves of, by the way. As well as the technology that it denies even exists.

So just another piece of real world data confirming the efficiency of plug-ins with larger battery packs. This was, admittedly, using a parallel hybrid as a starting point, but the all electric modes for parallels and hybrids is virtually identical. If anything, the larger motor on a series hybrid would deliver superior efficiency to the Prius’.

“Hybrid” mode is a bit more murky of a concept. Google.org lists 68.4mpg for its conversions, but its unclear if this is true miles per gallon, or miles per gallon EQUIVALENT. More likely the latter.