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Behind the Scenes: A Leaf Pioneer on the EV's Drive Magic

Way back before designs for the Nissan Leaf arrived it was the job of one engineer in Nissan’s EV Technology Development Division to work tirelessly exploring the potential for...

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2011/09/15

Way back before designs for the Nissan Leaf arrived it was the job of one engineer in Nissan's EV Technology Development Division to work tirelessly exploring the potential for the electric vehicle. That pioneer was Ken Ito, head of EV Powertrain Engineering Dept.

When Nissan CEO Carlos Ghosn rode in Ito's EV prototype he was grinning from cheek-to-cheek, with COO Toshiyuki Shiga likewise as jubilant as a child. There wasn't a person who rode in it that didn't find their hearts pounding with anticipation for the future of EVs.

But why? What is so special about the way they drive? The engineer who more than anyone was spellbound early on by EVs, tells all...

Smooth, Immediate Acceleration

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The benefits of electric vehicles are well known: they are clean and environmentally friendly; they are energy-efficient. But what are they actually like to drive?

Until recently, EVs were seen as inferior to gasoline automobiles. People thought of them like leisurely golf carts. However, the EVs of today are a completely different species. The time required from first stepping on the accelerator to moving smoothly away is a mere tenth of a second. This level of acceleration - so fast you can barely sense it - means that an EV feels in fact like a whole new breed of vehicle.

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This graph shows the time from stepping on the accelerator pedal to reaching actual acceleration for both EV and gasoline engine vehicles. The red line on the graph, the gasoline engine, clearly shows how acceleration overshoots for a while before settling at the best level. However, take a look at the blue line (the Leaf). You can see that, in stark contrast, the acceleration performance is very smooth right from the start.

Ito says we tend to feel that the "red" acceleration is the one that's best, because we presume there should be a delay after stepping on a gasoline engine accelerator; a sequence of hitting the gas, then a lag, and finally power kicking in. An EV, though, can accelerate in a tenth of a second so there's no overshoot. You have complete control of the acceleration, serving up a whole different kind of driving experience.

Indispensable "Seasoning"

Anyone who has been in a Leaf probably thinks all EVs run just as smoothly. But actually, it only manages to achieve such a natural drive by precise control of its motor. The motor control settings determine what kind of drive you will end up with, and that's why at Nissan the inverters and motors used in EVs are all designed internally. Ito says you often hear that because EVs have few parts compared to gasoline engine automobiles anyone can manufacture them. But simply sticking together a motor, inverter and battery won't produce an EV that drives smoothly.

And with EVs, just like with gasoline motorcars, some "seasoning" is vital for supplying the kind of drive performance you want. For example, take the GT-R, Nissan's high-power supercar. While its price is a mere third of Ferrari's top model and the Porsche Turbo, it currently holds the course record at Nürburgring and is considered the world number one in terms of speed.

With an ordinary EV today, though, being fast wasn't the key concern for Ito and his team so much as working out how they could achieve a strong sensation of acceleration, and an intuitive, natural driving experience.

Batteries: The Key to EV Evolution

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One of the EV's star attractions, and a reason why the advanced models of today were not possible until now, is its battery. Storage cells preserve and deliver energy; usually the bigger and heavier they are, the more capacity they have. Creating small but high-capacity batteries has now allowed Nissan to extend EV driving ranges to fully practical levels - a major factor leading to the commercialization of the EV.

It's not only about range, though.

The Nissan Leaf is also equipped with special tools for utilizing this battery effectively. For example, there's a timer function controlled by a cellphone, so you can activate the air-conditioning before departure. In other words, the vehicle temperature setting can be adjusted in advance. And if you use your household electricity as your power source, then you don't even need to use the Leaf's battery and there's no impact at all on your driving range.

The air inside the car is also hermetically sealed so once you've warmed it up, it cools down more slowly. If you maintain the in-car temperature like this, then you don't consume additional power from the car for heating.

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But despite its strengths, the battery still presents the EV's next challenge. Current batteries are not able to perform at adequate efficiency during very low temperature. At normal temperatures they can store and deliver electrical power very quickly, but when the temperature drops the internal resistance increases and slows down the electricity output. Essentially this means that the charging speed and the car's ability to accelerate deteriorates.

The Nissan Leaf is engineered, however, to always deliver the minimum power necessary for a working drive even at -30°C (-22°F). Say it was cold enough for snow to pile up in Tokyo, it would still be possible to drive just like in summer conditions.

Now the next big target is to realize that same constant drive performance for even the coldest climates.

The "Super Leaf"

There is another dimension to the EV: its high energy conversion efficiency.

Gasoline motor engines can claim at most 97-98%, and on average only around 95%. But the EV has an energy conversion efficiency close to 100%. In actual fact, since there is loss from the inverter unit that converts the current, the total energy conversion efficiency becomes around 90% - but from this 90% there is almost no energy loss.
The EV prototype Ito built was about 1.5 times the power of the current Nissan Leaf. Ito tells of one episode that really illustrates the car's performance. COO Toshiyuki Shiga was driving the prototype through the test track tunnel and in front was a GT-R. After letting the GT-R drive ahead for a while, Shiga then put his foot down on the accelerator and in one breath had overtaken it. Shiga was completely over the moon and his elation remained at full-throttle for two or three more circuits.

But the drive performance of the prototype was different to the current Nissan Leaf. For that reason, people who rode in the prototype always say that the new Leaf's tuning feels mild. This is because for a prototype they specifically targeted a high-power result. However, this creates many issues, such as the load on the battery increasing too much and so on.

Production vehicles, though, require production vehicle-style "seasoning". So Nissan designed the Leaf as a quiet, smooth-running automobile for a broad range of drivers.

EVs have a lot of potential that gasoline cars simply don't have. But as things stand, for power there is still no match for large displacement gasoline vehicles, even though actually powering up a motor itself is not difficult. There's no question that if Ito and others can fully realize the potential of storage batteries for power and additional capacity, then it's possible to get a driving experience equal to any high-performance gasoline car.

That, then, is Ito's next dream: Someday making a high-power "Super Leaf".