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Thursday, December 29, 2011

Close-up Look @ the Wheel Motor powered SIM-LEI [video]

The SIM-LEI, an electric car developed by a spin-off startup at Keio University in Tokyo in collaboration with a total of 34 domestic and foreign companies, says it is on track to start mass-producing the vehicle in about 2 years.

The LEI can travel 333 kilometres (207 miles) on a single charge of it's 24.5 kWh battery, which is approx the same battery capacity as that found in the Nissan Leaf. SIM Drive said the LEI (“Leading Efficiency In-Wheel motor”) recorded an electrical power consumption of only 77Wh/km during JC-08 mode tests. (for comparison, a Nissan LEAF consumes 120Wh/km in JC-08 mode).

A brief run down on electric vehicle dynamics to explain how this vehicle achieves 77 Wh/km.

The car is equipped with a 65 kW / 700 Nm Outer Rotor BLDC PM Wheel Motor in each wheel (260 kW / 2800 Nm total). These Direct Drive wheel motors eliminate the 20-30% energy loss common to a typical automotive mechanical transmission system. This direct drive energy efficiency gain translates into a matching increase in brake energy regeneration potential and that potential is multiplied by the SIM-LEI being all wheel drive, meaning it collects the maximum available regenerated energy compared to a 2WD EV (70% of vehicle braking is on the front axle).

The JC-08 test represents driving in congested city traffic, including idling periods and frequently alternating acceleration and deceleration, providing plentiful opportunity for brake regeneration.

The JC08 is conducted on a chassis dynamometer so does not test the SIM-LEI's aerodynamics which at Cd 0.19 is the same as the tear drop shaped GM EV1 and is significantly better than the 0.28 Cd achieved by either the Volt or Leaf. Considering drag (and resulting energy loss due to aero friction) is proportional to the square of speed, it becomes clear that the SIM-LEI has been designed from the ground up to be a seriously energy efficient EV.

If the SIM-LEI went into production with a range equal to the Nissan Leaf it would require a battery pack with perhaps only half the kWh capacity, potentially halving the cost of the most expensive component in the vehicle and making the purchase price of EVs more affordable.

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