Tesla Engineer Boosts EV Range to New Heights

When Carol Straubel's 14-year-old son was re-building an old electric golf cart in 1989, she found herself driving the boy from town to town in Wisconsin, sometimes as far as 50 miles, in search of batteries, tires and electric motors.

"He was passionate about it," Straubel recalls. "He wrote to the manufacturers for information. He worked on it every day, all day long, all evening long, until he got it to run."

What Straubel didn't know back then was that her son, "JB" Straubel, would still be on a motor-and-battery mission 20 years later. JB Straubel, now the chief technical officer of Tesla Motors Inc., is the winner of the 2009 Design News Engineer of the Year award, largely because he's as obsessed with electric vehicles today as he was when he and his mother were crisscrossing Wisconsin in search of golf cart parts in 1989.

The difference, though, is that the 2009 version of JB Straubel is now applying that same fire and passion to a mission that's meaningful not just to him, but also to the global auto industry and to the nation, as well.

"It really feels like we're trying to change the world," says JB Straubel (JB stands for Jeffrey Brian; he prefers not to punctuate it) of his company's task. "There's a real David and Goliath feel to it."

If the task of changing the world is daunting, however, that hasn't stopped Straubel and his fellow engineers at Tesla. Before rolling out the prototype Tesla Roadster in 2006, the company's engineering staff set their sites on an incredibly ambitious 250-mile battery-only range for the vehicle, and then came within a hair of meeting it. The Roadster's final, EPA-verfied, 244-mile range was approximately three times that of the now infamous General Motors EV1, which hit the streets a decade earlier. 

That stunning achievement not only turned heads among such competitors as General Motors, it set the stage for the emergence of electric vehicles in a way that hadn't been expected yet by the automotive community. At the time, most engineers wondered aloud about the range and costs of electric vehicles (EVs), especially since no production cars had yet reached 150 miles, let alone 244.

"It would have been substantially easier to make a car that was quick, handled well, and did everything else the Roadster does, but had 150 miles of range," Straubel says now. "But holding the bar at the 200-mile level was something that was critical to changing perceptions about EVs. From the earliest days, it was something we set out to do."

A Bigger Vision

For Straubel, however, taking aim at daunting EV goals now looks more like a matter of destiny than determination. Since finding the rusty, 30-year-old golf cart in an Egg Harbor, Wisconsin, junkyard 20 years ago, Straubel appears to have been on a trajectory that would inevitably land him in world of vehicle engineering. While still in junior high school, he built a working hover craft for a science fair. Another time, he commandeered his family leaf blower to construct a blow furnace, which he used to melt aluminum, although it was never clear why a pre-high-school-age boy needed molten aluminum.

"JB was born to be an engineer," Carol Straubel recalls. "He was always passionate about anything that had wheels and required engineering."

Not surprisingly, Straubel's college days also neatly positioned him for the world of alternate propulsion. At Stanford University's School of Engineering he created his own academic major in energy systems engineering and earned a master's degree in it.

"It was a great fit for me because it let me follow my passion," Straubel says now. "It's kind of eerie to see how my career has followed what I wanted to do at the time."

Straubel joined Tesla at the ground-floor level in 2004 after stints at Rosen Motors, which built hybrid powertrains for cars, and after attempting to start his own company aimed at creating electric airplanes. Before arriving at Tesla, he also worked with Stanford colleagues on a solar vehicle racing team and kept in touch with friends at AC Propulsion, which built an electric sports car capable of going from 0 to 60 mph in under four seconds. No matter what Straubel did, electric propulsion was always at the core.

"I was talking to anyone and everyone to promote the idea that EVs had turned a corner," Straubel recalls. "I told them that with new battery technology, they could go much, much farther than anyone thought was possible. I wanted to demonstrate my ideas in a working vehicle and break a few perceptions."

Through his aerospace connections, Straubel eventually met PayPal entrepreneur Elon Musk and described his ideas. Musk subsequently invested in Tesla Motors (which was looking for an initial round of funding) and brought the 29-year-old Straubel on board as chief technology officer.

"Elon had a much bigger vision for (the company)," Straubel says. "It aligned so well with what I was already doing that it was impossible not to get excited."

Reality Strikes

For Tesla Motors, however, the transition from a loose group of Silicon Valley rebels to automobile manufacturer was not an easy one. Suddenly, the company's engineers had to worry about issues such as manufacturability, reliability, safety and cost. The idea of building a high-end, high-performance, electrically-powered two-seat vehicle now looked more daunting, especially since the new engineering team had almost no experience in the auto industry.

From the beginning, however, Straubel had no intention of backing off his primary goal, which was to build a car with enough range to change those public perceptions.     

"We wanted a 250-mile range," Straubel recalls. "That was the number we were gunning for from Day One."

Led by Straubel, the engineering team began by picking a small form-factor lithium-ion battery cell, like those used in consumer electronics. In all, Tesla engineers employed more than 6,800 of the cells, which measure 18 mm in diameter by 65 mm long (slightly larger than a AA battery), in a pack that weighs about 450 kg (990 lbs). By combining thousands of small cells, rather a few huge ones, the engineering team was able to maximize heat removal because the smaller cells offered vastly more surface area, they say. In a white paper on the subject, Tesla's engineering team explains that the surface area of the 6,800 batteries is 27 square meters - about seven times more than if they had used 20 large batteries. That means they have about seven times more area for heat transfer at the surface of the cells.

Moreover, Straubel and other Tesla engineers teamed up to create a patented cooling system that mitigates the possibility of thermal runaway - a phenomenon that has been known to happen, however rarely, in laptops and other consumer electronic products that use lithium-ion. Tesla's cooling system uses a manifold and cooling tubes to run a 50/50 mix of water and glycol through the pack, drawing heat away from the batteries. As a result, the possibility of a cell sparking and setting a neighbor afire is dramatically diminished.

"As the energy density of these cells increases, the number of packaging and cooling problems increases," Straubel says. "You're trying to package a lot more energy into a much tighter space and suddenly cooling becomes a big issue."

Pulling The Right Levers

Despite the engineers' best efforts on the battery, however, Straubel and his team quickly found that they were still falling far short of their 250-mile goal. Even with a battery pack energy density approaching 200 W-hr/kg, Straubel says, the vehicle initially achieved a range of about 170 miles. Worse, there was no obvious culprit to blame for the shortfall.

"It's one of those classic problems where there's not a single major solution," he says. "It really takes a broad systems-level viewpoint to understand all the little ‘levers' you have, and to understand that you can pull 10 or 15 small levers to get a good outcome in the end."

Indeed, Tesla's team pulled a multitude of those "levers" to reach their goal. Primary among those was improving the vehicle's aerodynamics, decreasing its rolling resistance, changing the brake calipers, adjusting tire pressure and switching from a two-speed to a single-speed gearbox.

For Straubel, the stickiest of those problems was the gearbox. Early on, the engineering team had envisioned the high-performance vehicle as a two-speed, despite the fact that an EV's torque curve enables it to work in a single-speed configuration. Over time, the engineering team ran into difficulties, the biggest one being that the vehicle was far less efficient than they had expected. Engineers argued whether the extra gears, clutches and weight were really a benefit to the vehicle.  

"We sat around a table and said, ‘Look, we'd be better off with a single speed vehicle where we put more focus on increased torque and power out of the motor, rather than relying on this old-world solution of complicated gearboxes and moving mechanical parts,'" Straubel recalls. "In hindsight, it was absolutely the right thing to do."

The engineering team also squeezed out a tiny bit more range by employing a so-called a "roll-back seal caliper" in the brakes. The device, which pulls the caliper away from the disc when the brakes are released, eliminates residual drag forces between the caliper and disc when the brakes aren't being actuated.

Straubel says that the caliper and other small fixes enabled Tesla to boost its range toward to the 250 range. EPA tests on a dynamometer by a third-party vendor verified that the Roadster achieved a total range of 244 miles.

"At some level, you're always hoping to do better," Straubel says of the fact that their effort fell short of 250. "But we were happy to get to 244."

Man On A Mission

Colleagues say that Tesla couldn't have done it without Straubel's quiet leadership. Straubel stayed the course on their goal of 250 miles and was flexible when the team needed him to be, they say.

"When a strategy doesn't appear to be working, JB is able to stop on a dime and change the company direction," notes Kurt Kelty, director of energy storage systems for Tesla. "Not only is he able to change his own direction, he's able to rally everyone around him to support the new direction."

Most important of all, Straubel's dedication to the EV cause seems to be the result of a strongly held set of beliefs. Kelty says he has witnessed Straubel's sense of cause, even outside the confines of Tesla. "I've caught him on business trips changing light bulbs in hotels to CFLs (compact fluorescent lamps)," he says. "He has even bought a box of light bulbs and provided the box to the hotel manager and shown him how easy it is to make the change."

"JB is at Tesla because he believes it's the best place to put his efforts in order to make electric vehicles happen," adds Drew Baglino, senior electrical engineer at Tesla. "He really does think that this is where he can make the most impact on a problem that the U.S. and the industrialized world has."

Straubel's efforts to change perception of EVs are evidently working. After Tesla earned some measure of public success with its stellar EPA rating, former GM executive Bob Lutz admitted to changing his mind about electrics. "They have a real shot at success," Lutz told Newsweek magazine in December, 2007. "Their Roadster, if and when fully reliable, is an extremely attractive proposition."

To be sure, the road hasn't always been smooth for Tesla, and multiple stumbling blocks still lie in its path. In November, 2008, Newsweek pointed out that Tesla was traversing a rocky road after its first 40 Roadsters went out of the factory with drivetrains that needed to be replaced. The company has also been beset by messy firings and legal entanglements, and a few reviewers have complained that the vehicle isn't reaching its 244-mile range (A Wall Street Journal review said the vehicle achieved ranges of approximately 144 and 168 miles). Moreover, price tags for early Roadsters have passed the $100,000 mark, making it a more logical choice for wealthy celebrities like George Clooney and Matt Damon than for middle-class Americans.

Still, reviewers have been generally positive. Car and Driver, Edmunds.com, and Automobile Magazine, among others, have been enamored with the vehicle, especially its 3.9-second 0-to-60 mph acceleration. It has "smooth with amazing acceleration, comfortable seats, and plenty of head and leg room," notes Design News reader Stuart Koford of Cincinnati, OH, who owns a Roadster. "No problems so far."

Straubel, however, won't be satisfied until he can change more of those public perceptions about EVs. Recently, Tesla announced that it will produce a seven-seat sedan called the Model S, which will offer a variety of ranges up to 300 miles, starting at $49,900 in 2011. By going to larger production volumes, Straubel believes he can drive the battery price down to $300/kW-hr, ultimately placing pack cost "in the ballpark" of $18,000. That, he says, would help cut the overall cost of the car. For now, however, Straubel plans keep pushing the mileage envelope. Challenges like those are what keep him going, say those who know him best.

"To find a place to do what he loves is amazing," notes Carol Straubel. "And to have it matter to so many is that much better."

Read about the runners up for Design News' 2009 Engineer of the Year!