How It Works
The Tesla Roadster powertrain consists of four main parts: the battery pack (which we call Energy Storage System or ESS), motor, transmission, and the PEM (Power Electronics Module), none of which are “off-the-shelf” components. Rather, each includes innovations, both small and large, to support our mission of a high-performance car that’s gentle on the environment. Together, these four components form one of the most instrumented cars ever made.
Energy Storage System (ESS)
When you set out to build a high-performance electric car, the biggest challenge is obvious from the start: the battery. Its complexities are clear: it’s heavy, expensive, and offers limited power and range. Yet it has one quality that eclipses these disadvantages, and motivates you to keep working tirelessly: it’s clean.
The Tesla Roadster’s “fuel tank” weighs in at about 1,000 pounds and delivers four to five times the energy-density stores of other batteries. Safe, light, durable, and recyclable, it represents the biggest innovation in the Tesla Roadster and is one of the largest and most advanced lithium-ion battery packs in the world. Why this matters to you, the driver, is that it frees you to drive farther than ever before in an EV, while enjoying the power of world-class performance. The design ensures optimum operating conditions which maximize the life of the cells, while offering high levels of safety.
The architecture provides excellent redundancy and tolerance against cell-to-cell manufacturing variations. The system uses commodity lithium ion cells which, thanks to high demand by the consumer electronics industry, has spurred development that drives costs down and performance up. Finally, recharge time is impressively quick, enabled by an onboard, high-power charging system.
The system addresses thermal balancing with a liquid cooling circuit. Multiple passive and active safety devices ensure safe operation over the wide range of driving environments and scenarios. An array of sensors and a dozen microcontrollers communicate with the vehicle to allow efficient use and management of the battery pack. Finally, the entire assembly is housed in a rugged enclosure, which protects the system from the harsh road environment while supporting the internal components.
The ESS changes the very personality of electric cars — making the Tesla Roadster the first car that delivers the power of a sports car, the driving range of a gasoline-powered car, and the greenness of a bicycle.
Motor
The motor for a high-performance electric car requires a device that is simultaneously light, compact, and high in efficiency. The Tesla Roadster EV motor is just that. We accomplish this by starting with a well-optimized electromagnetic design and then using the lowest loss conductors and the highest quality magnetic steel possible.
The power of the motor is not only limited by how much power you put into it, but also by how fast it can be cooled, how hot it can operate, and how efficiently it runs. We addressed each of these in innovative ways. Our motor can operate continuously around 120°C, thanks to the array of air-cooling fins on our aluminum housing.
Without proper efficiency, our motor would convert electrical energy into heat instead of rotational energy. That’s why we constructed it with specially designed, high-quality lamination steel that has very low eddy current losses, particularly at high rpm. The rotor is made with a proprietary process that produces a low resistance “squirrel cage” with large end rings using oxygen free copper. This allows the rotor to develop high current flows, and torque, with low resistance losses. The use of a small air gap allows tight inductive coupling which, combined with low loss magnetic materials, enables the development of high torque at high rpm. Together, these factors allow us to induce large currents, even at high rpm, producing much flatter power and efficiency curves from approximately 2,000 rpm to 12,000 rpm.
The sum of all these features is a single motor with efficiencies of 85 to 95 percent, power output of up to 185 kW, and a small footprint that measures just 250 mm (diameter) by 350 mm (length).
Transmission
Inside the box, our transmission couples the simplicity and efficiency of a manual with the smarts and sophistication of an automatic. The Tesla Roadster has only two forward gears and either one will work for most of your driving. Unlike a manual transmission, the car will not stall if you have it in the wrong gear. Plus it puts you in control of the shifting to fine-tune your driving experience or to achieve the upper limits of acceleration and top speed. And because there is no clutch, you can quickly and easily start from a stop or shift gears on the freeway.
Power Electronics Module (PEM)
You’ll see this very important part of the car every time you pop the trunk. It controls over 200 kW of electrical power during peak acceleration, enough power to illuminate 2,000 incandescent lightbulbs (or 10,000 compact fluorescents). The PEM performs several critical functions in the Tesla Roadster, including motor torque control, regenerative braking control, and charging.
When you shift gears or accelerate in the Tesla Roadster, the PEM translates your commands into precisely timed voltages that tell the propulsion motor to respond with the proper speed and direction of rotation.
Circuits within the PEM monitor temperatures, voltages, and currents for maximum or minimum limits by using a combination of hardware- and firmware-settable values. These circuits prevent damage to the PEM, ESS, or motor when a variance from nominal operating conditions is detected.
During normal operation, the PEM monitors things like the voltage delivered by the ESS, the speed of rotation of the propulsion motor, and temperatures of the motor and power electronics. Should you like to know these things yourself, simply glance at the on-board Vehicle Display System.
Efficiency & Performance
Efficiency. Performance. Pick Two.
Gone are the days when sports cars demanded a choice between efficiency and performance. Now it’s no longer a zero-sum game. Instead, you get peak performance at every moment, with little mileage penalty.
Instant Freedom
The first time you drive the Tesla Roadster, prepare to be surprised. You’re at freeway speed in seconds without even thinking about it. There’s no clutch to contend with and no race-car driving techniques to perform. Just the touch of your foot and you’re off, without any of the sluggishness of an automatic.
How powerful is the acceleration? A quick story to illustrate. A favorite trick here at Tesla Motors is to invite a passenger along and ask him to turn on the radio. At the precise moment we ask, we accelerate. Our passenger simply can’t sit forward enough to reach the dials. But who needs music when you’re experiencing such a symphony of motion.
Rest assured that this responsiveness works at all speeds, as noticeable when you’re inching your way through parking lots as when flying along freeways.
100% Torque, 100% of the Time
The Tesla Roadster delivers full availability of performance every moment you are in the car, even while at a stoplight. Its peak torque begins at zero rpm and stays powerful beyond 13,000 rpm.
This is the precise opposite of what you experience with a gasoline engine, which has very little torque at a low rpm and only reaches peak torque in a narrow rpm range. This forces you to make frequent gear changes to maintain optimal torque. With the Tesla Roadster, you get great acceleration and the highest energy efficiency at the same time. All while requiring no special driving skills to enjoy it. This makes the Tesla Roadster six times as efficient as the best sports cars while producing one-tenth of the pollution.