The 77th Installment
Fuel Cell Vehicle “MIRAI” Production Line Tour
by Noboru Koyama,
Professor, Master Program of Innovation for Design and Engineering
I recently had the opportunity to visit the Toyota Mirai production line. The Mirai is the world’s first fuel cell vehicle (FCV). The line is at one corner of the Toyota Motomachi Plant in Aichi Prefecture, the first passenger car production plant in Japan.
The line is different from most lines in that it is designed for limited production vehicles. It was previously used for the LFA, Toyota’s first full-scale sports car, of which only 500 vehicles were produced for the entire world. I visited there once several years ago when it was still known as LFA Works.
I have decided to use this column to introduce usually unreleased information about the Mirai line.
The Mirai line at one corner of the Motomachi Plant was small enough to be viewed as a single entity. It was not a mechanized conveyer line but rather one in which the vehicle being assembled was pushed along by hand with the vehicle components efficiently positioned around it. The production rate is now 3 vehicles a day. However, an increase in production rate to 9 vehicles a day next year and a final further increase to 12 or 13 vehicles a day after that is planned. The highest figure will result in an annual production of 3,000 vehicles.
I was rather surprised to learn that only 13 employees were involved in the Mirai assembly process. Since the number of parts required for any vehicle do not change, each employee is responsible for the assembly of 30 to 40 times the number of parts that an employee on an ordinary assembly line would be. Both expertise and precision are required.
I observed a portion of the chassis assembly process. Each screw was individually tightened using a torque wrench.
Most challenging was the installation of the high-pressure hydrogen tank. Strict safety measures are taken to protect against a hydrogen explosion. Helium gas is used in place of dangerous hydrogen gas to check for leakage from the 18 tightening points. The work process continues as these many checks are made. The result is careful and sound assembly work.
My feeling is that much was learned from past LFA production line technology and know-how. The final assembly process involving the installation of the doors and other interior parts was carried out by 4 employees. A single employee installed all four doors in approximately 30 minutes.
Assembled vehicles are transported to the Honsha Plant where they are filled with hydrogen before being returned to the Motomachi Plant for approximately 1,200 inspection and running test procedures including wavy road operation performed on all vehicles. Only then are the vehicles released to the market.
Let’s consider the design and development of the Mirai. New car design and development requires an appealing theme without which things will not go well. The Mirai was every bit as difficult as the Prius.
Chief Designer Tomoyasu Nishi speaks of the “Shaping of wisdom” theme. The theme must boldly, cleverly, and accurately project the FCV system in a way that makes its innovative values obvious at a glance. Functional visualization from the perspective of the user is required. The user must come to realize the value of the vehicle through the diffusion of the maker’s plan in an easy to understand manner.
Air intake and water exhaust is expressed by a unique inverted triangular front grill symbolizing cooling air. Viewed from the side, the water droplet flow design of the body and passenger compartment express the vehicle concept. Whether this be good or bad, it does give the vehicle an iconic appearance that even children can appreciate. In the final analysis, the vehicle will be evaluated by the user.
The Mirai is said to be the ultimate eco-car. It is powered by electricity generated by a chemical reaction between its hydrogen fuel and oxygen. Only water is produced as a byproduct of this reaction. No carbon dioxide is emitted. Hydrogen exists in a nearly infinite quantity on earth. Its use as a fuel is a big step toward a sustainable society.
The idea for this sort of vehicle has been around for a very long time but was impractical for mass production. Toyota technological development now makes such a vehicle practical.
The biggest problem was that water generated during vehicle operation would freeze in the sub-zero environment of the fuel cell. Hydrogen would cease to flow and power generation would stop.
Mr. Manabe of the FC Technology and Development Department, one of the developers of the technology used in the Mirai describes what is happening when a fuel cell generates electricity in a sub-zero environment. Constant observation shows us that the water remained a liquid until it froze at somewhere below the freezing point. Power generation continued up to the point where the water actually froze. If some way could be found to restart fuel cell operation by heating the cell above the freezing point during this short time period, power generation would continue.
In fact, heating the fuel cells required a large heater which was impractical to install in a vehicle. Then came the idea of using the fuel cell itself as a heater.
The idea is to propel the vehicle with the highest efficiency possible. This brought about the “inversion concept” in which the vehicle is moved with ultra-low efficiency. In other words, it led to a “rapid warm-up operating point” that results in just enough power generation to drive the vehicle and enough heat generation to warm the fuel cells. It becomes possible to start fuel cell system operation even in very cold environments. This opened the way for mass production.
Mr. Manabe talks about his study of various technologies before the development of new fuel cell systems. “Point-to-point connection” of seemingly unrelated technologies was utilized to develop a new technology.
Toyota’s fuel cell technology won the Japan National Invention Award this past year. This award, established in 1926, was previously won by Sakichi Toyoda in that year and by Kiichiro Toyoda in 1938.
Many years have passed since then but the spirit of Sakichi Toyoda and Kiichiro Toyoda live on in Toyota products such as the Prius (the world’s first mass-produced hybrid vehicle sold throughout the world) and the Mirai. As I visited the Mirai production line, I felt the “point-to-point connection” between the earlier Toyodas and the present. I also sensed that fuel cell vehicles would become common in the near future.