Article Comments - 2009 Subaru Stella Plug-In Electric First Drive

2 messages, Last post on Jun 22, 2009 at 5:49 AM

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2009 Subaru Stella Plug-In Electric First Drive - First Impressions: More than just a science experiment, yet limited range and high cost will delay public acceptance. (more)

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#1 of 2 Article Comments - 2009 Subaru Stella Plug-In Electric First Drive by KarenS HOST Jun 19, 2009 (7:29 am)
Introduced to the press on June 4, the 2009 Subaru Stella Plug-In is on sale in Japan and deliveries will begin in August. The 2010 Mitsubishi i-MiEV goes into production in July, but it's going directly into use by a government fleet and won't be in the hands of private owners until April 2010. 2009 Subaru Stella Plug-In Electric First Drive Replies to this message: toyolla2 (Jun 22, 2009 5:49 am)
#2 of 2 Re: Article Comments - 2009 Subaru Stella Plug-In Electric First Drive [KarenS] by toyolla2 Jun 22, 2009 (5:49 am)
Replying to: KarenS (Jun 19, 2009 7:29 am) If you read up on Subaru's website for the WRX STI sport ute it appears that their drivetrain philosophy is always geared, if you will excuse the pun, towards the best way. Starting with a 6 cylinder horizontally opposed (boxer style) engine on the WRX which is mounted longitudinally its transmission feeds into a prop shaft down to the rear differential as per any RWD. Except that this being a full time AWD requires a transfer case and a front differential. These two units are combined rather neatly in the front transmission assembly. This results in a balanced system with a symmetrical layout and a low centre of gravity. When we come to the i-MiEV Stella plug-in things seem a lot less sophisticated. The electric motor is mounted on the engine crankshaft and feeds through a CVT, I assume, and is much similar to Honda's Integrated Motor Assist class of parallel hybrid. Two things prevent calling this a mild hybrid however. The fact that the 9.2KWhr battery holds seven times more energy than that of the Prius and the fitting of a 47Kw electric motor has ensured a comfortable performance in electric only mode as the review noted. The power capability of the larger battery will not only allow sustained driving at 60mph without damage to the battery but have capacity for considerably more regenerative braking than the 10Kw of the Prius. I assumed the electric motor is directly coupled to the crankshaft. This would account for the torque upgrade from 68lbs-ft to 110lbs-ft ( before engine modification that is). The parallel hybrid has the disadvantage that if the engine and electric motor are directly coupled then the engine and the electric motor will be rotating together even in electric-only mode. There are also the additional losses going through the mechanical.CVT which a pure EV doesn't have. OTOH the use of a CVT means that the electric motor won't have to drive the crankshaft at high rpms once cruising speed is reached. The CVT will adjust appropriately one hopes. There is also the matter of the requirement for a Reverse mechanical gear as it may not be permissible for the engine to be rotated backwards by the motor. This is a cost effective way to implement a parallel hybrid where the traction motor doubles as a generator and also provides starter motor duty for the engine. It is however not the best way since when operating as an EV the frictional engine losses and those of the CVT are borne by the electric motor. The best way is to go the series hybrid route. Of course the bad news there is that you now need to pick up the additional cost of the powerful generator needed to supply the motor. Not completely bad news however since the generator need only be a quarter of the size of the motor it has to supply. But even that cost could be offset by dispensing with the CVT and the reverse gear. Finally I have to say that Subaru's four cylinder supercharged engine is a mighty complicated way to get 63Hp. At the current state-of-the-art even a Yamaha 450cc single cylinder dirt bike engine can do that ! T2