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Code Word: Suisui! EV Driving Comfort Technology

Anyone who’s ever driven a Nissan LEAF knows just how smooth it feels – an experience realized by the car’s precise control of electric motor torque. But what is this control technology? NTM finds out...

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2012/03/25

Every day, people move around without a lot of conscious mental effort. After all, there’s no need for your brain to trouble itself telling your legs and body how to walk. We walk because we just want to go forward, and the need to do so unconsciously moves the muscles in our bodies. Our brain is actually sending out intricate commands for our hands and feet, and so on. One might call this a kind of “control technology.”

Torque Control: The Secret Behind LEAF’s Smooth Drive

In the same way, Nissan LEAF also helps control motion without you realizing it. LEAF is equipped with many controls set up to enhance the car’s effortless handling and drive performance.

One such control is a torque control system that uses advanced electric motor management to minutely adjust the torque increase and decrease in an extremely short time, in order to ensure smooth operation and good ride characteristics. In principle, stepping on the accelerator pedal will increase the torque and weight transfers to the rear suspension, causing the front of the vehicle to lift up. Taking your foot off the accelerator pedal decreases the torque, meaning the front of the car will lower (see Diagram 1).

Diagram 1

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As the torque of the drive wheels increases, the weight transfer causes the front of the vehicle to rise up. A lessening of the torque of the drive wheel means the weight shift is negated, and the vehicle’s front end will lower.
For example, when a car goes over a bump on a road surface the car body will vibrate. LEAF’s torque control system uses sensors to estimate the vibrations in the car body, and by then increasing and decreasing the torque, the vibration will be reduced. The torque control here is precise and minute, so the driver will feel little to no adjustment.

Likewise, torque control can be used to an advantage when driving around a curve or changing lanes in an EV. In addition to the strong grip all the tires have through vibration control, since steering is controlled through the drive wheels in a front-wheel drive vehicle like LEAF, the effects of increasing or decreasing rotation moment are utilized through the increase and decrease of the torque (Diagram 2).


Diagram 2

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When the steering wheel torque increases, the yaw moment on the car body increases. As torque decreases, the resisting torque on the car body will increase.
Torque is seamlessly controlled as soon as the driver turns the steering wheel, so that the driver can turn the car normally. Of course, since the car body vibrations are also being mitigated, we get a very smooth rotating movement. Any wobble you might experience when you return the steering wheel is also reduced by torque control. (Diagram 3).

Diagram 3

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The secret to LEAF’s smooth drive: Nissan LEAF has a high-response motor, with torque control to one hundredth of a second, and creating cornering performance that is smooth and easy.
This control technology is also effective when making a series of turns, such as changing lanes, seamlessly matching driver input. The result is precise steering and enjoyable handling characteristics for the driver.

Torque Control Brings Out the Motor’s Features

EVs are powered by electric motors, which have instant torque that is easy to control. Nissan LEAF showcases the EV motor’s strengths through its control technology, making a truly smooth drive a reality. The word the engineers use to describe this is “suisui”, which means “smooth” – much like the graceful gliding motion of a dolphin or pond-skater insect.

“A car’s concept is very important for vehicle development,” says Hiroki Sasaki. “LEAF’s identity, just how on earth this new kind of EV car would drive – we thought about all this from scratch, and we arrived at the driving sensation of ‘suisui’. The engineers in charge of the control technology were required to feel what a ‘suisui’ drive is, and have the knack for putting that into the actual car. The engineer needs to be able to imagine what he or she has to make a reality.”

Motor control technology can present challenges, though, and the primary objective of any manufacturer should be the driving experience. Nissan’s challenge is always to develop technology in a way that makes driving more enjoyable and efficient for the customer. Nissan’s engineering mission, then, is to apply appropriate controls that feel natural and avoids any excessive intervention

Ultimately, the only way to know if we have created a truly “suisui” smooth drive, is determined by real drivers on real roads. LEAF’s control systems were tested over many long test drives under all kinds of conditions, and input from the whole engineering team was processed. In the end, the team felt that anyone could feel the “suisui” drive in the LEAF.

“The aim of the test drive is, of course, to bring out the performance of the car,” explains Satoshi Ota. “And to check there is no movement that is different to the driver’s intentions, and that there is no discomfort for the driver. Our target is to develop motor control that our customers are satisfied with.”

Nissan’s Evolving EVs, Seeking New Possibilities for the Future

An EV motor generates instant torque, and even from the standpoint of torque control, it is a source of great potential for good driving characteristics. In tune with the concept of the car, by making all the vehicle’s parts and controls fully consistent, we can bring out the electric motor’s true capabilities. Control technology is the nucleus in the development of EV driving enjoyment.

“Just as the makeup of the car is decided with the vehicle concept in mind, so too is it necessary to create the control toward a goal,” says Hiroki Sasaki. “Depending on the kind of car you are aiming for, car ‘paraphernalia’ and control need to match that concept.”

EV driving performance is expanding toward new horizons. EVs like LEAF NISMO RC or the city commuter PIVO 3 are just two of many possibilities. What kind of “drive” will the EV serve up for us in the future? One thing’s for sure. Thanks to control technology, the EV’s prospects are boundless.


Learn more about Nissan LEAF control technology: watch NTM TV Vol.3 Driving Comfort