Story 1
For MIRAI—For the Future
Chapter 1

Development of the Air Compressor—This Started from 1993

Masato Sowa

Group No. 1, Planning Office
R&D Management Dept.
R&D Headquarters

Seeking an Alternative to the Scroll Type

Toyota Industries' history with air compressors follows their development of FCVs—this started back in 1993. The Technology Development Center was engaged in developing hydrogen-storage alloy tanks and hydrogen gas aspiration pumps, but because the hydrogen gas aspiration pump was a reciprocating type*2, it did not meet modern standards for performance, noise, or vibration (NV). Accordingly in 1997, the Technology Development Center requested that the Compressor Division develop a hydrogen gas aspiration pump. The following year we changed from a reciprocating type to a scroll type*3, and started development, also employing a scroll type compressor for the air compressor. These products were incorporated in the Toyota FCHV released at the end of 2002.

We continued with improvements to the scroll type, also using this on the Toyota FCHV-adv released in 2008. However, by this time, the development team had already started looking for a replacement to the scroll type, given its low compression range, which limited the amount of air (and consequently oxygen) that it could send. This was a structural problem, and we anticipated that the scroll type would not be able to respond to future demands for ever-smaller, lighter, lower cost, and low NV products. We examined various methods, and decided to adopt the "helical root type" rotor in its stead.

*2: Reciprocating type
This is the original type of air compressor in which a piston reciprocates in a cylinder to compress air. This operates at a low speed, with significant noise and vibration, however it is low cost.

*3: Scroll type
This refers to another method for compressing air within an air compressor. This comprises a pair of spirals—one fixed and one that moves in a circular motion, thus compressing the air. These are frequently used in automobiles and household air conditioning.

Helical Root Type
Development of the Air Compressor

The Next Step—the "Helical Root Type"

The helical root type rotates two root-style helical rotors, and this provides a smaller, lighter, and simpler construction. Our selecting the helical root type was the point at which our development accelerated. Masato Sowa talked to us about that time.

"The roots type is also called a "rotary blower," and they were known mainly for their performance as blowers rather than as compressors. Helical root type rotors are currently used in water treatment facilities and for conveying powder such as cement. Put simply, the helical root type method is capable of smooth and efficient transport of air, water, and powder, and these have not been used much for compressing air."

What About...

So why did we end up using the helical root type in an air compressor?

"We discovered air could be compressed depending on the number of lobes on the rotor, as well as on the twist angle." When using CAD*4, we discovered that changing the number of lobes and the twist angle reduced the amount of air taken in. And so... after repeated experiments and calculations, we arrived at figures that achieved our objectives."

Although Mr. Sowa explained this calmly, what he was describing was the very essence of innovation! The helical root type, which had up until that point not really been considered for air compression was given new value by being employed in an air compressor, as a result of the dedicated experimentation by Mr. Sowa and his group, and the new perspectives that they unearthed.

*4: CAD
Abbreviation of Computer Aided Design. Design work on a computer, formerly performed by hand.

Outstanding Performance

The team then fully investigated lobe numbers and twist angles, ending up with specifications that maximized efficiency. With the air compressor in hand, they finally set their sights on the competition—in which Toyota Motor Corporation decides which product to use in their FCV.

"At this study meeting, we first announced the data from the air compressor. When we announced our figures, there was quite a commotion from the other competing companies. It was only at this point that we realized that our product had overwhelmingly better performance."

Mr. Sowa grinned happily, remembering the smile on the face of a Toyoya Motor Corporation's project general manager.

"We had reported our progress on the development of the helical root type to the project general manager numerous times—weekly, for several months. I'm sure he was worried as well, as to whether we could produce the results that were needed. However, we were happy that we could present our results, and just watching the smile on the face of the project general manager made it all worthwhile."

Winning this competition meant that Toyota Industries was commissioned to manufacture the air compressor for use in the MIRAI. This was a major step, rewarding them for their efforts in development, but a long road still lay ahead.

(Source: Toyota Motor Corporation website