Flipping the Switch on Electric Car Design

Designing a vehicle, whether a sports car or SUV, generally involves a core set of engineering challenges. There are issues around how to achieve great styling that appeals to the target audience along with complexities associated with optimizing performance — and zillions of others in between. Swap out the internal combustion engine for electric power and the hurdles multiply. The engineering team has to contend with the traditional set of design objectives along with new challenges in the areas of aerodynamics, packaging and power.

Part of what makes electric vehicle design more difficult is the fact it’s relatively virgin territory, with many of the core components like battery technology, power train modules and motors still evolving. “The biggest issue with electric vehicle design has to do with the level of maturity of components available,” says Andrew Farah, vehicle chief engineer on General Motor’s Chevy Volt concept electric vehicle. “There is no high volume yet for things like batteries and motors, which makes it a very unique issue for packaging all of this and getting it integrated physically into the vehicle while still maintaining the desired exterior and interior appearance.”

Just as with traditional vehicle design programs, 3-D technologies like CAD and simulation software are playing a huge role in helping large OEMs like GM and boutique electric carmakers tackle some of these challenges. Specifically, 3-D CAD tools enable the construction of full digital mock-ups of the vehicle, allowing manufacturers to modify and manipulate components for optimal packaging far before they build a physical prototype, which is costly to modify. Computer-aided engineering (CAE) software, including finite element analysis (FEA) and computational fluid dynamics (CFD) are also enlisted to fine-tune the aerodynamic nature of the vehicles and to analyze the various structures for optimal weight and materials makeup.

Aerodynamics, in particular, plays a much greater role in electric vehicle design than it does with a traditional gasoline-powered car. Because the power in an electric vehicle is derived from the batteries onboard, there is a constant trade-off between adding more horsepower (i.e., more batteries) and the toll that additional weight will take on the vehicle’s range and maximum speed.

“The impact of the duration you can run the electric-powered vehicle or the range you have is much more critical than the mileage you get out of a gasoline-powered vehicle,” says Peter Schmitt, vice president of sales, automotive business transformation at Dassault Systèmes. “It’s the key inhibitor today for embracing electric vehicles — the battery technology is not at a point where people feel confident.”

CAE analysis also plays a role in the structural analysis of these vehicles, helping companies model components in such a way that minimizes their size and weight, yet doesn’t compromise the integrity of the vehicle. This is particularly important because many of these electric vehicles are toting around hundreds, even over a thousand pounds of battery weight. “Weight is the enemy of efficiency,” says Dave Taylor, senior director worldwide automotive marketing for Siemens PLM Software, a maker of CAE and CAD software. “In a gas-powered vehicle, you’re working to get the most miles per gallon. In a battery-powered vehicle, you want the most distance between charges and every ounce works against you.”

Design News reached out to some of the more prominent electric vehicle projects to hear firsthand accounts on how they handled some of these challenges. Here are their stories:

Piecing Together the Tango

When you’re building a car that’s only 3 ft wide — and calls for nearly 1,100 lb of batteries onboard — getting all of the high-tech componentry to fit in a limited space is much like piecing together a puzzle.

That was one of the primary challenges Commuter Cars faced when designing its ultra-narrow Tango, an urban, commuter electric vehicle that, given its unique size and shape, can fit in a 6-ft half-lane and park in leftover spaces between vehicles. “It’s a tremendous challenge to pack all of the features of a full-size car into one quarter of the space,” says Rick Woodbury, president and founder of Commuter Cars, in Spokane, WA. “Every piece has to fit in with no space left around it. There isn’t another car out there with space more at a premium than ours.”

SolidWorks’ 3-D CAD tool was instrumental in helping Commuter Cars see in advance, in a digital format, whether things would fit, before building any physical prototypes. Early on, for example, the engineering team was able to determine that the original motor and transmission design didn’t work in the space allotted. It then used SolidWorks to create a unique two-motor design, which allowed it to better accommodate the batteries and air conditioning mechanics. “We had to design the whole car around the battery compartment and what we achieved by the two-motor design was that it allowed the rest of the bottom of the car to be devoted to the batteries,” Woodbury says.

Another major design challenge was getting the weight low enough to balance the car so it has the same rollover threshold as a sports car. The Tango, which can travel from 0 to 60 mph in 4 sec, extensively employs stainless steel and carbon fiber materials. Woodbury says SolidWorks’ Cosmos simulation software will have a role in helping Commuter Cars lighten up the car’s structure a little going forward.

The Tango is priced starting at $108,000, so Woodbury says the design objectives had to strive for optimal performance along with providing a lot of the extras people are accustomed to on higher-end, luxury vehicles. “If you’re going to build a car that’s so different and so small, you have to do a lot of justifications, especially in this price range,” he says. “CAD has been a godsend.”

Aerodynamics and the Chevy Volt

Her colleagues call Nina Tortosa the “aero police.” Tortosa, E-Flex performance engineer on General Motors' Chevy Volt concept car, is responsible for ensuring the production version of the electric vehicle has the optimal aerodynamics.

While GM engineers touched on aerodynamics for the concept car, the issue is now a top priority as the Volt team hones the initial design for production, with the goal of getting the car on the road by November 2010. The Volt team is trying to maintain the elements that made the car resonate with consumers when it was unveiled last year — for instance, the shape of the front grill, the shape of the headlamps and the body formation — while adding the all-important dimension of aerodynamics.

As a result, Tortosa and team were brought in far earlier in the design process and are now spending hundreds of hours in a wind tunnel and honing computer simulations to achieve a Volt design that performs. “The biggest difference with an electric vehicle is that aerodynamics becomes a much bigger contributor to fuel efficiency or electric range,” she says. “You can’t compromise on aerodynamics as you would in a traditional vehicle.”

Yet, to ensure the aerodynamics team doesn’t compromise shape, Tortosa and crew spend lots of time in the wind tunnel in the company of the studio designers so everyone stays in check. Along with the wind tunnel sessions, the Volt team enlists Fluent CFD software, now part of ANSYS, to do similar surface testing and flow visualization to zero in on problem areas and to identify issues that are harder to detect in the wind tunnel, she says. Already, some of the Volt’s design characteristics have changed since the aggressive testing, including rounder, less square front corners, according to Bob Boniface, GM’s director of E-Flex Systems Design.

Along with aerodynamics, packaging is more of a challenge in an electric vehicle, according to Farah. Because there are few off-the-shelf components and because you’re attempting to fit elements like motors and batteries into an already established space, the design is much more fluid. “It introduces very difficult physical integration challenges because you have a desired exterior design surface and an interior design surface and the space in between,” he says. “You’re trying to develop the component sets at the same time you’re trying to fit everything together.”

Performance Trumps Practicality

From the get-go, the vision for the Tesla Roadster has been all about performance. Given the price premium that consumers would have to pay for still-emerging electric vehicle technology and the fact that torque of the platform lends itself to a sports car, Tesla engineers weren’t looking for anything practical in the design.

“This is not the punishment car — people aren’t going to drive it because they have to,” says Barrie Dickinson, Tesla’s director of body engineering.

With 0 to 60 mph in under 4 sec and 100 percent electric as core goals, Tesla engineers faced trade-off between style and performance that were more arduous than with a traditional gasoline-powered vehicle design. “With electric vehicles, aerodynamic losses become significant in terms of range,” Dickinson says. “You need a good aerodynamic package and performance, which is something most sports cars don’t worry too much about. They normally worry about styling and whether there’s a good balance in terms of lift. We needed to keep our drag relatively low.”

In order to do that, Tesla enlisted the help of MIRA, a UK-based consultancy that specializes in vehicle design. MIRA built CFD models of the Roadster and tapped wind tunnel technology to refine its aerodynamic performance. FEA analysis software is also part of the game to reduce mass on components wherever possible, Dickinson says. While the basic structure of the Tesla Roadster’s structure comes by way of a partnership with Lotus Cars, Dickinson says FEA analysis helped the company re-engineer the chassis in a number of areas, including the side rail of the car and the inside door. “We use analysis to ensure that we’re as light as we can be while hitting all of our performance requirements in terms of stiffness and strength,” he says.

Dassault Systèmes’ CATIA and digital mock-up capabilities helped from a packaging standpoint to fit the car’s nearly 1,000 lb of on-board battery power. The initial designs called for a smaller battery pack, but as new safety features and other capabilities were introduced, the power requirements kept increasing, which led to on-going changes. “Using CAD and digital mock-up allows us to react to those changes a lot more effectively as opposed to having to do things in a more manual way,” Dickinson says.

The Tesla Roadster went into production March 17.

Redesigning for Electric

While aerodynamics, packaging and power concerns are design issues for Zenn Motor Cars, they take a back seat to the company’s biggest challenge: Rearchitecting host vehicles to run on electric power.

Zenn’s core competence is in electrical engineering and systems integration, hence its strategy to work with suppliers. Zenn converts the host vehicle’s drive train into an electric offering and readies the design for production, not a one-off conversion. “So much is happening in energy storage and environmental concerns that speed to market becomes increasingly important,” says Michael Bergeron, Zenn’s vice president of engineering. “Smaller companies don’t stand a chance from the ground up.”

Zenn’s first vehicle conversion is a limited range vehicle, with maximum speeds of up to 25 miles an hour, for short, local trips. Trying to convert an existing vehicle with existing systems into an electric vehicle is a challenge because many of the systems such as power steering racks or ABS braking aren’t harmonious to electric power, Bergeron says. “One of the challenges is what features and functions shall we put into the drive train that are not part of the drive train itself,” he says. “The base vehicle already has the wiring harness and major components designed and it’s crucial for us to take those systems, understand them and convert them to electrical in CAD.”

Design tools from Mentor Graphics and Dassault’s CATIA facilitated a lot of this conversion work prior to producing a prototype. Specialized analysis software also helped Zenn engineers determine how to reuse existing air flows to do some of the necessary cooling for the batteries, and 3-D modeling was employed to model all the devices, fit them together and see the impact on the center of the gravity. CAD tools also allowed the Zenn team to design in some styling elements, including the addition of digital readouts and gadgets to play up the high-tech feel of the vehicle.

One of the biggest differences between electric and traditional vehicle design is the need to be more exact. “We’re trying to design closer to the edge than internal combustion engines so there’s a greater reliance of the modeling because we need to be more precise,” Bergeron says. “As an industry, we’re all battling the internal combustion engine hangover where the speedometer on the car goes way higher than you could ever legally drive. We’re trying to be more focused on the range of speeds required.”