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Basic Building Blocks for EVs

You can purpose build or you can spread your risks when developing a car powered by electricity.
#Infiniti #Ford #Nissan


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Once upon a time, we had the GM EV1, a ground-up dedicated electric vehicle (EV) that shared little to nothing with its volume-production brethren. As much science experiment as transportation device, it combined unique materials, techniques and styling with an electric drive system and battery pack designed to meet a mandate California eventually rescinded. Until the Nissan Leaf and Mitsubishi i-MIEV arrived on the scene, no other major automaker would attempt to build a unique electric car for sale to the public. Even then, these were not the only answers to building a modern EV. After all, not everything needs to be different.

The Pragmatic Approach
No one knows how deep or robust the nascent EV market will be, and whether demand will profitably support multiple entries. One way to reduce the risk—and the overall investment—is to build an EV on an existing platform. That way, some 95% of the parts can be used for the conventionally powered vehicles for which the demand is a bit more predictable. This is the route Ford has followed with the Focus Electric.

Listen to Ford’s Shawn Lightner, Global Program Manager, Focus Electric, and you almost get the feeling that building an electric vehicle is, in a word, simple. “You pull out the internal combustion engine, and put in a package that is much smaller than the one you’ve just removed,” he begins. “There’s the inverter, the electric motor, and the computer controls. You keep the exact same cooling system as the gasoline car.” The main battery pack sits under the rear seat in place of the gas tank, while another pack sits in the cargo area behind the rear seat where it affects cargo space and brings total output to 24 kWh. The charger packages where the catalyst normally lives. “We had to add stiffeners and some structure to hold the batteries and meet rear crash standards,” he says, “but the modifications were minimal.”

What really makes the Focus Electric work, however, is the fact that Ford heavily invested in designing, developing and building hybrid vehicles. “There was a lot to build on already,” explains Lightner. “You’re building on many of the same systems, and it helps to have experience with them in order to get them to work effectively together and to the highest efficiency.” This included things like the Smart Gauge to check energy use, including energy recovery while braking. The regenerative brakes are the same as those on the Fusion Hybrid and C-Max, but putting energy back into the system is critical for range. Communicating this became crucial. “We visited EV enthusiast clubs, and we met with guys who built their own EVs,” says Lightner. We even went to visit aerospace clubs to look at the human-machine interface, because if you run out of fuel when you’re flying…”

Built (Almost) From Scratch Optimism
Renault-Nissan took another path. It created an EV-specific platform for use on Nissan, Infiniti and Renault models, and amortized costs over three brands. Though volumes for each vehicle may not be high by industry standards, together they allow an EV family to be built profitably. Starting with its B Platform, engineers in Japan basically replaced everything between the A- and C-pillars. This let them retain the MacPherson strut front and torsion beam rear suspensions, crash structures and cargo space of the conventionally powered versions, and insert a battery optimized passenger compartment.

Forty-eight modules of four battery cells each are packaged under the floor of the Leaf, the Nissan EV available in the U.S. market. The rear cells are stacked on their side, while those under the front seats and rear footwell lay flat. All are packaged in a singular structure whose frame is bolted to the bottom of the car. This makes future battery swapping relatively simple, should Nissan decide to go down that road. It also keeps the weight of the air-cooled 24-kWh lithium-ion battery pack down and within the wheelbase. Thus, the center of gravity is low, and the effects on handling are minimal. The lack of water cooling, however, means the battery pack can see capacity and range reduced in extreme heat.

The Future
Other than demand, the main determi-nant of EV viability will be battery technology. How small and powerful battery packs can get will determine how much range and power can be packaged into a vehicle. It will be joined by decreases in charging time, though there is concern that too much quick charging will adversely affect battery capacity and life. According to Lightner: “It’s not a hard and fast rule that, if you push x amount of energy through, you will get y degradation.” Also, there’s still a lot of work to be done on EV standards, including reconciling the SAE and Japan Electric Vehicle standards for Class 3 chargers and plug design. However, work also continues on inductive charging, first seen on GM’s EV1, though Lightner suggests this iteration may take the form of charging pads you park an EV over in your garage, and “Blue Sky” stuff like integrating charging pads into roadways so EVs can get charged on the fly. “There’s a lot of controls and safety type of things that have to be worked out,” he says, “but the technology continues to move forward and affect hybrids as well as EVs.”

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