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Friday, June 19, 2009

Closer look at the Subaru Stella Plug-In electric vehicle

Since Subaru announced the world's first mass production lithium ion battery powered plug in electric vehicle would go on sale next month, a few motoring publications have got their hands on one if only very briefly. Edmunds took it for a spin but the contributor obviously is not up to speed technically on Evs as he kept referring to the cars constantly variable transmission (CVT). As with all Evs the Stella has a single speed reduction gearbox for maximum energy efficiency to the wheels and because the 47 Kw (63 hp) BLDC electric motor has 170 Nm (125 ft/lb) from zero rpm. took an early prototype for a spin in February and the Stella EV has some interesting features. The gear lever the Edmunds writer was confusing with a CVT is actually use to adjust the level of brake regeneration the driver prefers. With the 'transmission' lever in D the car drives with mild regen. Putting the lever into L engages heavy brake regeneration and the Subaru EV can be driven in city traffic almost completely without using the friction brakes at all.

There are a couple of unfamiliar gauges in the instrument cluster. Replacing the fuel gauge is a battery charge gauge with increments in km. Interestingly it is not a linear scale as while 'full' is 80 km, 2/3rds full equals 30 km range. The second new gauge shows how much power the motor is drawing or returning to the batteries.

The Stella Ev tops out at a max speed of 100 kph (60 mph) which Subaru say helps keep to energy consumption in check and the batteries cool. Seeing as around 100 kph is expressway speed in most countries it seems a reasonable limit for an urban commuter car. The Stella body shell isn't the most aerodynamic we've ever seen and as aero load increases as the square root of speed (i.e. double your speed and you quadruple the wind resistance) the shape of the car, no doubt, has a lot to do with the imposed speed limit.

Range from the small 9.2 kWh battery pack of 90 km (55 miles) is quite impressive when you keep in mind that much like the Chevy Volt, not all the battery capacity is used. In the Volt only 8 kWh of the 16 kWh capacity is actually usable.

It is believed Hitachi Maxell are the suppliers of the high performance Lithium Ion batteries found in the Subaru Stella EV. The battery will accept an 80% charge in as little as 15 minutes or take 4 hours to charge with a 240 volt outlet. Perhaps the best part of owning an EV is how much they cost to run. To 'fill' the Stella will cost less than $1.00 @ $0.10 kWh. The additional weight of the battery only ads 120 kg to the car compared with the ICE version and curb weight is still in the 'lightweight' range of around 1000 kg.

Ten points to Subaru for being first to launch a production li-ion battery powered EV while other car companies, noticeably Toyota, who even in their 3rd generation Hybrid still don't sell either a plug-in or lithium ion batteries.

While some headlines have focused on the relatively expensive purchase price of these new Evs due to the very new technology in the batteries, if you add up your fuel costs with an ICE powered car over the life of the vehicle, in many cases you will have paid more to fuel the car than you did to purchase the car in the first place.

Plug-in Stella specifications:
Dimensions (Length x Width x Height): 3395mm ×1475 ×1660
Curb weight: 1060 kg
Passenger seating: Four
Maximum speed: 100km/h
Per-charge driving distance: 80km
Electric motor: Permanent magnet synchronous motor
Max. power output: 40kW
Max. torque: 150Nm
Drive-train: Front-wheel drive
Battery type: Lithium-ion batteries
Total voltage: 346V
Total energy capacity: 9.2kWh

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