Simple Powertrain Improves Efficiency And Reliability For Tesla Roadster

SAN CARLOS, Calif. (July 19, 2006) — Every moving part of a vehicle's propulsion system reduces its efficiency, so Tesla Motors's electric motor has only one moving part. Compare that to a typical American sports car's V-8 engine, with eight pistons, eight connecting rods, a crankshaft, 32 valves, oil pumps, valve springs and many more moving parts. Which one is likely to be more efficient? And which one is going to be more reliable?

The electric motor's efficiency rating is likely to be as high as 95 percent, while the internal combustion engine's efficiency is 20 percent or less. With this efficiency, the Tesla Roadster achieves the equivalent of 135 mpg.

That efficiency doesn't slow this sleek sports car down, either. Estimated 0-60 mph time is around four seconds, and with an electric motor, the torque is instantaneous, throw-you-back-in-the-seat responsive.

The 3-phase, 4-pole AC induction motor has a rotating magnetic field. Through electromagnetic induction, the rotating magnetic field induces a current in the conductors in the rotor, which in turn sets up a counterbalancing magnetic field that causes the rotor to turn in the direction the field is rotating. The rotor, which is made of copper and non-magnetized steel, provides power through the transmission to drive the rear wheels of the Tesla Roadster. The top speed for the motor is 13,500 rpm, putting it in Formula One territory, about twice the typical "red-line" of IC engines. The motor can deliver about 185 kW to the transmission.

The computer-controlled system for the motor, known as the Power Electronics Module (PEM), is an integrated power inverter and high-rate charging system. The motor can provide negative torque, otherwise known as regenerative braking, to enhance range. During charging the maximum input power is 240 volts at 70 amps AC 45-65 Hz or about 17 kilowatts. The PEM is air-cooled.

The unique two-speed electrically actuated manual transmission is also designed for optimum efficiency, with an integral free differential and final drive. There is no external oil cooling required. The transmission is cooled internally with a splash lubrication system. The gearshift is electro-mechanical with an electro-mechanical transmission lock (park position) on the final drive. There is no clutch. Torque change and speed matching for shifting is done using computer software. Maximum torque is 260Nm and maximum input speed is 13,500 rpm. Since electric motors can run in either direction, there's no need for the additional weight from a "reverse" gear; a simple switching arrangement reverses the motor. An on-board controller provides traction control.

All performance numbers are preliminary. Tesla Motors is currently involved in important and time-consuming safety and durability testing for the Tesla Roadster. While we are confident of our numbers, this testing may require design changes that affect the final specifications. Mpg is for the EPA highway driving cycle. Conversion from electric consumption to gallons of gasoline equivalent is calculated using the EPA conversion factor documented in the Federal Register: June 12, 2000 (Volume 65, Number 113), Rules and Regulations, Pages 36985-36992.

About Tesla Motors

Tesla Motors was founded in July 2003 by Martin Eberhard and Marc Tarpenning to create efficient electric cars for people who love to drive. The Chairman of Tesla Motors, a privately held company, is Elon Musk, who has led or co-led all three rounds of investment resulting in $60 million in funding. Mr. Musk has been instrumental in both corporate and product development at Tesla Motors.

The company currently employs over 80 people, including teams in California, the U.K. and Taiwan. The background and experience of Tesla Motors's employees mirrors the vehicle itself, drawing from diverse expertise in the electronics, automotive and software industries.

Tesla Motors creates vehicles that conform to all U.S. safety, environmental and durability standards. Tesla Motors's cars include modern safety equipment such as airbags, front crumple zones, side impact protection, and 2½ mph bumpers. Tesla Motors will only sell cars in the U.S. when they pass the Federal Motor Vehicle Safety Standard (FMVSS).

For more information, visit www.teslamotors.com.