|On the Nordschleife. Click to enlarge.|
The racing driver Sabine Schmitz has tested the battery-electric Furtive eGT sports car from Exagon Motors (earlier post) on the Nordschleife (north loop) of the Nürburgring, achieving a top speed of nearly 240 km/h (149 mph) on the 20 kilometer long Nordschleife. The Furtive eGT, introduced earlier this year at the Paris Motor Show, features motors from Siemens and batteries from Saft.
Exagon intends to build a small production series of the Furtive eGT starting in 2013. Siemens, which has cooperated for a number of years with Exagon at the Andros Ice Race for electric vehicles, says it views the Furtive eGT sports car as an opportunity to demonstrate the efficiency and performance of its motor technology. The Siemens global research unit Corporate Technology developed the powertrain and built a prototype.
At 52 kg (115 lbs), the motor used in the eGT is one of the lightest and most compact units on the market. During the test on the Nordschleife, it produced 125 kW of power—which is to be increased to 148 kW for the production version. The eGT is equipped with two, for a combined output of 296 kW (402 hp).
The liquid-cooled motors are centrally mounted and linked up with a novel WCT (Without Cut Torque) three-speed gearbox, which harmonizes well with the Siemens’ control strategy for rapid shifting. On each gear change, one of the two motors continues to transmit power to the wheels. This process avoids any break in torque to maintain power in all circumstances. Furthermore, the motors function continuously within their optimum range of power and efficiency, enabling the vehicle to take full advantage of their power and to increase energy efficiency.
The engineers of Exagon Motors developed this gearbox specially for an electric motor. Unlike other supercars fitted with sequential gearboxes, the Furtive-eGT runs no risk of the clutch breaking in the event of violent acceleration. It is designed for use without a clutch, either in manual mode with the steering-wheel mounted paddles or in automatic mode. For reverse gear, the rotational direction of the motors is inverted.
With a constant 516 N·m (380 lb-ft) of torque from 0 to 5,000 rpm, the Furtive-eGT accelerates from 0 to 100 km/h in 3.5 seconds. Top speed on the racetrack will be 287 kilometers per hour (178 mph); on public roads the speed will be limited to 250 km/h (155 mph).
The 360V Saft battery pack has a capacity of 53 kWh; it is spec’d to retain more than 80% capacity after 3,000 charging cycles—enough to take the car one more 1 million kilometers.
Two inverters, also developed specially for the Furtive-eGT, distribute electric power by converting the direct current from the Saft battery into alternating current. The inverters drive the motors in two modes, based on torque or engine speed, modifying amplitude and frequency as necessary. The “supervisor” control electronics were developed internally by Exagon.
Projected range for the Furtive eGT is:
- 360 km (224 miles) over an urban cycle (ECE15 standard).
- 310 km (193 miles) over a combined cycle (NEDC standard).
- 287 km (178 miles) over a highway cycle (EUDC standard).
An optional range extender combustion engine can increases the overall range of the Furtive-eGT to 807 km (501 miles) with 25 liters of fuel over a standard ECE15 cycle, or 734 km (456 miles) with 25 liters of fuel over a standard combined cycle.
To meet a full range of driver requirements, depending on vehicle use, the engineers at Exagon Motors developed four operating modes for a personalized driving experience: Standard, Eco, City and Sport.
In Sport mode, the emphasis is squarely on performance and sport driving, with specific accelerator response, acceleration control and motor speed for gear changing.
In Standard mode the motors function normally, delivering full power and optimizing motor speed for gear changing, to improve efficiency and focus on driveability.
In Eco mode, the power of the motors and peripheral electricity-consuming functions are limited in order to place greater emphasis on range and to make the Furtive-eGT easier to handle by an uninitiated driver.
In City mode, vehicle operation is optimized for low speeds, with the emphasis on smooth driving. The air in the cabin is recycled automatically to reduce the nuisance caused by exhaust gases from other vehicles.
The Furtive eGT features a carbon-fiber body; an aluminum rear cradle supports the motors, gearbox and power electronics. The architecture of the carbon body made it possible to install the batteries in the floor of the Furtive-eGT. This lowers the center of gravity (110 mm lower than on a conventional GT) to virtually eliminate roll on cornering, for exceptional ride and handling.