of Europe brings an element of hope and possible revival to the flagging fortunes of the electric car with the first use of lithium-ion (Li-ion) batteries in a road vehicle by a major player in the industry. The high energy density and power-to-weight ratio of these storage units puts a prototype electric version of the small Ka hatchback on a par with the gasoline-powered model in driving performance. Top speed is said to be 82 mph (132 km/h) with acceleration to 62 mph (100 km/h) in 12.7 seconds, although range between charges still is only 95 miles (153 km), but extendible to 125 miles (201 km) with a constant speed of 48 mph (77 km/h).
Until now, Li-ion batteries have been used mainly in small consumer electronic products like notebook computers, cellular phones, baby monitors and smoke detectors. Output per cell of 3.6 volts is some three times that of nickel-cadmium (Ni-Cad) and nickel metal-hydride (NiMH) that they widely replace. They also retain full charge regardless of usage, can be recharged from zero to full capacity in six hours, handle some 3,000 repeated charge/discharge cycles, and are immune from the so-called “memory effect” suffered by Ni-Cads.
The basic Li-ion chemistry was initially redeveloped for automotive use by the French company SAFT SA, a leading battery manufacturer. Their advanced technology was then adapted to the e-Ka by's Research Center in Aachen, Germany, with financial assistance for the project from the German Ministry for Education and Research. The battery pack, consisting of 180 cells with 28 kWh rating, weighs only 615 lbs. (280 kg). This is just 30% the weight of the power equivalent in lead/acid batteries, and substantially less than comparable Ni-Cads and NiMHs. In terms of volume, the Li-ion has approximately half the bulk of all the other three.
Batteries are divided into three individual sealed “troughs” in the car, each with 30 modules containing six cells. One trough is located in the engine compartment, with the other two on either side of the back axle. Nominal output of 315 volts DC is transformed by a solid-state inverter to three-phase AC for the traction motor. Heat generated by the internal resistance of these second-generation Li-ion batteries is dissipated by one of two fluid cooling systems. A second independent system cools the drivetrain, with a 65-kW (88-hp) asynchronous motor followed by a fixed-ratio transmission driving the front wheels. Torque rating is 140 lb.-ft. (190 Nm).
Performance of the e-Ka is enhanced by a 100-lb. (45-kg) weight reduction to counter the battery load. The roof and hood are of aluminum sandwich construction with a thermoplastic filling, while the front brake calipers are paired with ceramic discs. e-Ka's wheel rims and back axle all are in light alloy. Electric power steering supplied byprovides further weight saving, where an electronic control module regulates the assistance needed to minimize battery demand. The brake servo and ABS system also are electric, as are the heater and windows.