Interview: Future Cars Will Be Like Trains

Youichi Hori, professor of Electrical Control System Engineering, Department of Informatics and Electronics at the Institute of Industrial Science, the University of Tokyo

- With the development of automotive electronics, how will cars change in the next 10 to 20 years?

The biggest change will be that cars themselves will be electric-powered, diluting the meaning of the word "automotive electronics." It's not that electricity or software will change cars but that cars themselves will become electricity, so to speak.

In other words, cars will be linked to electric power systems in the future. And it is becoming more and more likely that gasoline vehicles will change into hybrid and plug-in hybrid cars, and then into pure electric cars.

Of course, there are other possibilities like clean diesel cars and bio fuel cars though fuel-cell vehicles exist to the side of them, I would say. But trains proved one hundred years ago that electric motors are better actuators for conveyances if there is enough infrastructure to supply electricity.

When viewed in this light, the trend shifting from hybrid cars to plug-in hybrid cars and to pure electric cars is becoming more and more prominent. This trend will become even stronger after the G8 Hokkaido-Toyako Summit though it is also being influenced by soring oil price.

When cars are linked to electric power systems, their characteristics will change. I mean, they will be charged with a small amount of electricity at a time and will be charged more often. In other words, they will become like trains.

What's the difference between trains and cars? Trains move while being supplied with energy from outside. And cars run carrying most of the energy they need.

Currently, cars run 400-500km (250-313 miles) on a single fueling and at a maximum speed of 160km (100 miles) per hour because auto makers have made efforts to develop cars that can be used anytime, anywhere and by anyone.

However, do all cars really have to have those capabilities? Considering how they are used in reality, I think many people would be satisfied with cars that can run 20km (13 miles) a day and at a maximum speed of 100km (63 miles) per hour.

The travel distance of 400-500km is long enough to drive in the middle of the Sahara desert. It does not make sense to use that kind of car in urban areas.

When I talk about a car that can store little energy, people often ask me, "what will you do if it runs out of energy?" But, how many people drive to the areas where they cannot recharge their cars until the cars stop? We just need cars that meet our needs.

- What kind of electronic technologies are the keys to realize those evolutions of cars?

If cars are linked to electric power systems and run by frequent recharges, capacitors will gain in importance. Unlike trains, when cars are driven by electricity, they cannot be charged by using overhead wires stretched along roads. And they cannot carry around enough energy source to run 400-500km, unlike gasoline-fueled vehicles.

So, we have to build an infrastructure that can frequently recharge cars with a small amount of energy at a time. As for cars, all they need are devices for quick recharge and discharge.

Then, which is a better energy source for plug-in hybrid vehicles, secondary battery or capacitor? I would go with capacitor because it has a high current capability and can be quickly charged. The discharging rates of secondary batteries are high, but it takes time to charge them.

For example, in the case of plug-in hybrid vehicles with secondary batteries, they need to be charged for one to two hours at home. Though some people say the charging time will be shortened to about 15 to 20 minutes in the near future, it's still long. In this respect, capacitors can be charged in about 30 seconds.

However, we should mount a small number of capacitors because it would take long to charge many of them.

There are more useful characteristics of capacitors. First, it has a long operating life because no chemical reaction occurs when it is being charged or discharged. Second, the remaining energy in a capacitor can be accurately known by checking its terminal voltage. Third, containing no heavy metal, it is more environmentally friendly. And there are more advantages of capacitor.

The energy density of capacitor is still lower than, for example, that of Li-ion secondary battery but may catch up with it due to technological advances in the future.

In my laboratory, we are developing one-seater electric vehicle "C-COMS," which runs only with electric double layer capacitors, as part of our research on future cars.