September/October 2008

Tesla Roadster

A look under the hood of the electric sports car that is generating a buzz.

By Kevin Bullis

Multimedia   Watch the Roadster in action.

With its first prototype, the Roadster, introduced in 2006, Tesla Motors ignited interest in electric cars not only as a way to save gas but as a high-performance alternative to some of the fastest sports cars. This year, Tesla started delivering production ­vehicles, based on the test car shown here. The car sells for $109,000--but costs only a couple of cents per mile to power.

1 . Electric Motor
Most electric cars have used direct-current electric motors that rely on permanent magnets. The motor in Tesla's Roadster doesn't have any magnets; instead, it uses stacks of patterned metal plates and wires that generate electromagnetic fields. Such motors, called alternating-current induction motors, were first advocated in the late 19th century by Nikola Tesla, for whom the company is named. The company picked AC induction motors because they're simple, reliable, and efficient at a wide range of speeds.

2. Transmission
The first version of the Roadster featured a two-speed transmission, the first gear for quick starts (0 to 60 miles per hour in under four seconds) and the second gear for top speeds (over 120 miles per hour). But problems with that transmission delayed production. Thanks to a redesigned motor and higher-performance transistors that deliver more power, it has been replaced by a single-speed transmission.

3. Power Electronics Module
The motor does two things: it converts electricity from the battery into torque for acceleration, and it helps slow the car during braking, converting some of the car's kinetic energy into electricity that's stored in the battery. A computer chip called the digital motor controller regulates the shuttling of power between the motor and battery. It can deliver acceleration so fast it hurts: Tesla's engineers had to dial back the power to achieve a smoother start.

4. Battery Pack
Tesla's engineers have wired together 6,831 small, cylindrical lithium-ion battery cells to deliver the power that accounts for the car's impressive acceleration and the energy storage that enables a driving range of more than 200 miles. Lithium-ion cells store far more energy than the nickel-metal hydride batteries used in previous gas-­electric hybrids. But they can be tricky to work with: in extremely rare cases, manufacturing defects cause them to catch fire without warning. A liquid cooling system in the Roadster's battery pack removes heat so rapidly that the combustion of one bad cell can't set off the rest.

5. Body and Frame
An aluminum frame and carbon-composite body panels keep the car lightweight. That helps extend its range.

To read more about Tesla Motors and their technology, click here.