The first performance electric car manufactured by Tesla Motors, the high-performance, zero-emissions Tesla Roadster, was unveiled before a throng of well-wishers, car buffs, and potential customers Wednesday evening during Tesla’s "Signature One Hundred" event at Barker Hangar.
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.
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).
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. 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.
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.
Safety - Protection from the Ground Up
A well-built car considers safety long before it meets up with slick surfaces or red-light runners. At Tesla, we talk in terms of “active” and “passive” safety, ensuring our cars are built to prevent a collision and to minimize damage should one be unavoidable. The car’s very design — with its low center of gravity and finely tuned steering — offers such stable wheel control that it drives like it’s on rails.
Four Outstanding Safety Features: The Tires
Most people rarely think about tires. At Tesla, we obsess about them. The reason is simple: when driving, tires are your only contact with the outside world. Keeping that contact steady, compliant, and with good grip is key to stability. The Tesla Roadster starts with superior Yokohama tires, and fits them onto custom and directional wheels. Our independent, double-wishbone suspension ensures that each wheel works independently with optimal tire-to-ground contact at all times. And because tire pressure is crucial to a balanced drive, our VDS (Vehicle Display System) comes standard with a tire-pressure monitoring system.
The Most Crucial Few Seconds Behind the Wheel
We’ve done everything in our power to minimize the likelihood of an accident. But no car manufacturer can prevent accidents. Should the unthinkable happen, you’ll be reassured to know that we’ve already thought about it, many times over. Our 4-channel ABS system offers shorter stopping distances and gives you full steering control with no lockup. The car’s side beams are positioned to offer extra safety to the exact area where you sit. Plus, we outfit every car with driver and passenger airbags, roll-over protection, and energy-absorbing sections in both the front and back of the vehicle.
For automakers the world over, keeping a vehicle’s occupants safe is a key factor when designing a car, particularly a performance electric car like the Tesla Roadster.
Tesla Motors’s designers and engineers have gone to great lengths to ensure that not only is the Tesla Roadster safe to drive, but also when charging the performance electric car, at home or on the road. Their goal is to not only meet, but to surpass the rigorous standards of the Federal Motor Vehicle Safety Standards, or FMVSS, as implemented by the National Highway Traffic Safety Administration (NHTSA).
"The Tesla Roadster will meet or exceed the FMVSS criteria, period," said Tesla Motors CEO Martin Eberhard. "From traditional items like seat belts, air bags, and anti-lock brakes, to EV-specific standards including electrical disconnect systems and color-coding high voltage wires, I expect this car to be a model for vehicles anywhere, electric or not."
NHTSA has a legislative mandate to issue Federal Motor Vehicle Safety Standards and Regulations to which vehicle manufacturers, like Tesla Motors, must conform and certify compliance. These Federal safety standards are regulations written in terms of minimum safety performance requirements for motor vehicles or equipment.
The FMVSS includes crash testing in order to fulfill the "occupant crash protection" standard (part 571, standard no. 208), which specifies performance requirements for the protection of vehicle occupants in crashes. Its purpose is to specify vehicle crashworthiness requirements in test crashes and static airbag deployment tests. This standard also specifies equipment guidelines for active and passive restraint systems.
The FMVSS also has standards specific to electric vehicles, including redundant, independent electrical disconnect systems, activated when the car’s electrical system has been compromised by a ground fault, too much current, over- or under-voltage, overheating, liquid in the energy storage system (ESS) or in the case of an accident.
The Tesla Roadster’s high voltage wires are color-coded in accordance with the FMVSS and feature double insulation. All high-voltage enclosures, including the ESS, feature tamper-proof packaging and warning labels.
The ESS, which provides power to the entire vehicle, features an independent safety system designed to disconnect power outside the ESS enclosure under a variety of detectable safety-threatening situations.
The Tesla Roadster comes complete with its Electric Vehicle Service Equipment (EVSE), a home-based charging system. The EVSE is only to be installed by a qualified electrical technician, and also features an automatic system to switch off the charging current prior to the removal of the charge lead connector. The home system also includes a smoke detector that will discontinue charging and cut off current to the charging system if smoke is detected. Similarly the home system is equipped with a system that detects any unusual tension on the charging cable (such as another car running over the cable) and will cut off current passing through the cable. The Tesla Roadster is equipped with a safety interface that prevents the car from being driven or even moving if the charging system is connected to the cars charge port.
More traditional vehicle safety apparatus include self-tensioning driver and passenger seat belts and shoulder straps. An audible alert and instrument panel warning light will activate in the event the driver’s seat belt is unfastened while driver key is inserted.
Passive safety is provided through energy-absorbing structure built into the front and rear of the vehicle, also known as "crumple zones," and driver and passenger air bags are also standard. The passenger compartment is encompassed by extruded aluminum door beams and high level side beams.
Enhanced safety features include the antilock braking system and traction control. An interlock system prevents the car from rolling or accidentally accelerating until the driver has turned the car on, fastened the seat belt, and shifted from park.
What has 6,831 non-moving parts and powers a car? It’s the unique Energy Storage System of the new Tesla Roadster.
The 6,831 non-moving parts are cells slightly larger than a typical AA battery. The large number of small cells allows Tesla Motors’s engineers to create an energy storage system around fixed points on the chassis, ensuring optimum efficiency in packaging.
Tesla Motors CTO JB Straubel said, "Maximizing battery run-time is critical for an electric vehicle, but we’ve been able to do just that with the Tesla Roadster while minimizing weight and maximizing safety. The proprietary technology developed at Tesla Motors for our Energy Storage System is critical to the success of the Tesla Roadster."
The Energy Storage System (ESS) provides power to the entire vehicle, including the motor. It comprises a durable and tamper-resistant enclosure, the 6,831 cells, mechanical structure to mount the batteries, electrical interconnection between the cells, interconnection to the power electronics unit, a network of microprocessors for maintaining charge balance and temperature monitoring, a cooling system, and an independent safety system that is designed to isolate high voltage outside the enclosure under a variety of detectable safety situations.
A cooling system is controlled by the vehicle electronics. It uses a secondary loop in the cabin air conditioning system to provide chilled coolant which is circulated throughout the ESS. A resistive heater is used to heat the batteries in extreme cold conditions.
Batteries using the same lithium-ion technology used in Tesla Motors’s vehicles have proven themselves over years of usage in modern electronic devices such as cell phones, camcorders, MP3 players and other digital devices. Unlike previous-generation nickel-cadmium and nickel-metal-hydride batteries, lithium-ion batteries have no "memory," and are good for 500 complete charge/discharge cycles before replacement may be required.
Lithium-ion cells are rechargeable and provide one of the best energy-to-weight ratios and a slow loss of charge when not in use. Pioneered by Gilbert N. Lewis in 1912, the first commercially available lithium-ion cell was created by Sony in 1991.
Lithium-ion technology is improving rapidly with the latest breakthroughs focusing on reducing charging time, and improving the capacity of cells. Tesla Motors continues to explore improvements in energy storage technologies and is actively working with several lithium-ion cell manufacturers.