Nissan Improving Leaf One Amp at a Time

The Ward’s 10 Best Engines competition has recognized outstanding powertrain development for 17 years. In this installment of the 2011 series, Ward’s looks at the development of the electric powertrain for the Nissan Leaf.

Okay, it’s not an engine. It’s a propulsion system.

Engineers took pains to make sure “engine” does not look too alien to consumers.

It’s a 107-hp, 207 lb.-ft. (280-Nm) battery-powered, all-electric propulsion system that delivers up to 100 miles (161 km) of range with Environmental Protection Agency equivalent fuel economy of 106/92 mpg (2.2-2.6 L/100 km) city/highway.

The closest it will get to a fuel-burning engine is in an owner’s garage (next to the unlimited-range vehicle) or in a public parking structure. But the name of the Ward’s 10 Best Engines competition is not changing. Thanks for asking.

If it puts power to the wheels of a new passenger vehicle, whatever is under the hood is eligible for a Ward’s 10 Best Engines award. And what’s powering the Nissan Leaf electric vehicle is good enough to win in its rookie year.

“The immediate low-end torque inherent to electric motors makes it lots of fun to drive,” Ward’s Associate Editor Christie Schweinsberg says.

“A blast to drive,” echoes Ward’s AutoWorld Editor-in-Chief Drew Winter, who calls the Leaf, “the first ‘pure’ EV with the potential for mass acceptance.” But he adds, “The car still needs improvements to mitigate the nervous emotion called range anxiety.” Mark Perry, product planning director-Nissan North America, tells Ward’s the motor’s history dates back to a battery breakthrough in 2003.

Nissan had been working on its own battery technology for more than a decade when it hit upon a new laminate construction and lithium-ion manganese chemistry. Four years of development later, the Leaf EV program began.

Nissan Leaf is small but roomy inside.

First, there was the decision whether to look to suppliers for major components – including the drive motor, power inverter and battery management system – or do it in-house. Going the latter route would require substantial investment, but Nissan believed the expense would be outweighed by better control over performance and cost.

There also was the issue of production scale. “Some (EV component) suppliers are not used to (high-volume) automotive scale,” so could we even find a supply base?” Perry recalls.

These unknowns led to the decision to vertically integrate and do the propulsion system all in-house.

The next big thing was to secure sufficient battery performance at a reasonable cost, with the understanding it would be a mass-market offering.

Then came a determination over vehicle architecture: whether to create a dedicated platform or convert a conventional vehicle to accommodate an electric powertrain.

“We went through that decision and decided to go dedicated (platform). Different (auto makers) are making different choices on that,” Perry says.

Choice of 3.3 kW vs. 6.6 kW onboard charger was cost, packaging decision.

The result of Nissan’s development process is a practical 5-door hatchback with compact-car performance and midsize roominess.

The challenge was to make the Leaf, which is extraordinary in so many ways, drive like a conventional car and achieve mass-market volumes, Perry says. “We could not compromise performance or customer amenities. This was not a test or demonstration project.”

The size and performance of the drive motor were key issues. “The size of the motor didn’t affect the jump off the line all that much, but it did affect passing,” Perry says.

“We started at one level and ended up at a higher level because of (the need for more) passing power. We wanted to give that peace of mind you get in an ICE (internal combustion engine): step on it, the transmission steps down, the engine roars and all that lovely torque shows up. But with an EV, (the power) is so linear. We wanted to make sure that folks would feel confident, with reserve power for passing.”

For regenerative braking, engineers strove to avoid the “grabbiness” often associated with EVs and hybrid-electric vehicle deceleration and braking. Instead, they aimed to deliver the normal coast-down feel of an ICE.

So what’s unique about the Leaf compared with other EVs?

“It’s on a dedicated platform, and it’s out there today,” Perry says. “There is nobody out there, and nobody forecast to come, who has a mass-market, zero emissions, no-gas, and no-oil offering that does what the Leaf does.”

The Ford Focus battery-electric vehicle (BEV), due late this year, does pack a faster 6.6 kW Level 2 (240V) onboard charger vs. the Leaf’s 3.3-kW unit. Speed is not that important for overnight home charging, but it is a big advantage for a lunch or shopping stop with Level 2 public charging.

“The choice of a 3.3 kW vs. a 6.6 kW onboard charger was a cost and packaging decision, and one we have been studying for years,” Nissan’s Perry says.

“We felt that for launch the combination of 110V, 240V at 3.3 kW and DC fast-charge capability was the best way to come to market. But it's not a difficult add, and we’ll respond to market demand, not competitive pressure.”

Ford says its Focus BEV will not offer DC fast-charging, at least at first, because there is no single U.S. standard for that technology.

“But there is an existing standard called CHAdeMO (an abbreviation of “Charge de Move”), a consortium of companies,” Perry says. “It’s the standard for Japan. It’s also in Europe and it is (Underwriters Laboratories)-certified and approved for the U.S. It’s rolling out across the country, and manufacturing companies are investing in it.”

Using that technology, Nissan touts the Leaf’s capability to DC fast-charge to 80% state-of-charge in less than 30 minutes.

“SAE in the U.S. has not yet decided on a standard,” Perry says. “But there are a lot of charging stations out there, and a lot of cars, from us and other manufacturers, that use this standard that’s already U.L. certified and in commercial development. So we advocate strongly that SAE needs to recognize that.”

Beyond charging improvements, battery-cost reduction and energy-density increases, there still are other opportunities to improve the Leaf’s powertrain, Perry says. “We think the battery pack design we have, both the chemistry and the laminate structure, is the best combination for today.”

“But we always get the question, ‘Is this going to be like an iPad, where a year after introduction there’s a new improved version that costs less and does more?’ With development times in the automotive world, it's a bit further out than that.”

With a BEV, auto makers have to go around the entire vehicle and look at every system. “It’s almost like Apollo 13,” Perry says, where desperate astronauts scavenged fractions of amps to power up the crippled spacecraft for reentry. “Every time they turned on a system, how much amperage was it using? We’ve done a lot of that, but there’s always room for improvement.

“In the motor and in systems like cabin comfort, it’s all about efficiencies. We use low-rolling-resistance tires, but is there another generation of tire in the future?

“You could use a lot of carbon fiber (to reduce vehicle weight) but not for (a car priced) under $30,000. We also have to work on reducing the gradual loss of capacity of the batteries over time. There is so much work to do to continue to improve.”

Renault-Nissan CEO (and strong BEV advocate) Carlos Ghosn says an auto maker must manufacture EVs in high volumes to be successful. He has set BEV targets of 500,000 and a million units as “stair steps” that will allow major cost reductions.

“We're trying to prepare for a world where the federal tax credit and other incentives may not exist,” Perry says. “And you know that to get $7,000 out of a car is a monumental task.”

Veteran auto engineers would agree that even a 10% cost reduction is huge. This will be an interesting process to watch over the next several years.