|The A1 e-tron. Click to enlarge.|
Audi’s A1 e-tron, introduced at the Geneva Motor Show (earlier post), is a range-extended electric city concept vehicle featuring a 75 kW (102 hp) peak power electric traction motor and a single-rotor single-rotor Wankel engine coupled with an electrical generator with a charge rating of up to 15 kW.
The four-passenger, two-door mega city vehicle (MCV) car can drive 50 kilometers (31 miles) emission-free in city traffic on its 12 kWh battery pack before the range extender kicks in. The Audi A1 e-tron was designed specifically for use in the metropolitan areas of Europe and North America and in the rapidly growing megacities of Asia and South America.
Motor and power electronics. The synchronous electric motor of the Audi A1 e-tron is mounted transversely at the front of the car. Its low mounting position has a positive effect on the vehicle’s center of gravity. Continuous output is rated at 45 kW (61 hp), with peak power of 75 kW (102 hp) available in short bursts. 150 N·m (111 lb-ft) of torque is continuously available, and peak torque is 240 N·m (177 lb-ft).
The electric motor sends its power to the front wheels via a single-speed transmission. The retractable selector lever on the console of the center tunnel used to choose between “Drive,” “Reverse,” and “Neutral” was taken from the first Audi e-tron.
The power electronics are mounted in the engine compartment above the electric motor. The most important components are the pulse-controlled inverter, which serves as the controller between the electric motor and the battery; the DC converter, which connects the high-voltage network with the 14 volt electrical system; a breaker unit to protect the high-voltage components; and the charging module.
Audi has developed a proprietary thermal management system to keep the battery, the electric motor, and the power electronics within their respective ideal temperature windows.
The socket for the standard charging plug is located behind the rings in the single-frame grille of the Audi A1 e-tron. A fully depleted battery can be recharged in approximately three hours from the 380 volt grid. A display immediately adjacent to the plug-in connection shows the current charge status and the charging time remaining.
The concept of the innovative Mega City Vehicle requires the electrification of key auxiliaries. The refrigerant compressor of the climate control system, for example, is electrically powered by a high-voltage electric motor that supplies only the amount of power needed at the time.
This increases system efficiency substantially compared to conventional concepts. Via a special circuit, the climate control loop also functions as a heat pump that regulates the temperature of the cabin and the battery.
The power steering of the Audi A1 e-tron is electro-mechanical. An electronic brake system makes it possible to tap into the recuperation potential of the electric motors. A hydraulic fixed-caliper brake is mounted on the front axle, with two novel electrically-actuated floating-caliper brakes mounted on the rear axle. These floating calipers are actuated not by any mechanical or hydraulic transfer elements, but rather by wire (“brake by wire”). This eliminates frictional losses due to residual slip when the brakes are not being applied. In addition, the servo unit received a new, demand-controlled electric vacuum pump.
Battery pack. The energy storage unit is arranged below the floor, assisting with the center of gravity and weight distribution of the vehicle. The battery pack is shaped like a T, with the short transverse beam filling the rear section of the center tunnel and the cross-beam filling that area in front of the rear axle where the fuel tank is otherwise located.
The 380 volt lithium-ion rechargeable battery has a nominal energy content of 12 kWh. It comprises 96 prismatic cells and weighs less than 150 kilograms (331 lbs).
|The range extender engine with its cooling fins displayed under a sheet of glass in the luggage compartment. Click to enlarge.|
Range extender. The A1 e-tron concept car has a Wankel engine as a range extender, but other compact concepts are also possible. The small single-rotor Wankel has a chamber volume of 254 cc and runs at a constant 5,000 rpm in its peak efficiency window. The electronics also consider navigation data such as the destination and route profile to automatically activate the range extender as needed.
The driver can also turn the range extender on and off as necessary with the push of a button The fuel tank holds 12 liters (3.17 US gallons).
Strengths of the Wankel engine include its nearly vibration-free and quiet operation, the small dimensions, and the extremely low weight. Together with the generator, which is powered by the Wankel engine and produces 15 kW of electric power, the complete assembly weighs only around 70 kilograms (154 lbs). This weight also includes the special power electronics, the intake, exhaust, and cooling unit, plus the insulation and the subframe.
Performance. The vehicle accelerates from 0 to 100 km/h (62 mph) in 10.2 seconds and has a top speed of more than 130 km/h (81 mph). The Audi A1 e-tron can also cover longer distances if the range extender charges the battery. The extra range, which is intended primarily for interurban driving, is 200 kilometers (124 miles).
According to the draft standard, the two different operating modes yield a fuel consumption of 1.9 L/100 km (123.80 US mpg), which corresponds to CO2 emissions of 45 g/km (72 g/mile). In electric mode, there are zero local CO2 emissions.