Our Stories 01 Development of Hydrogen Leak Detection Sensors

Story 01Innovative Development of Hydrogen Leak Detection Sensors
- Improving both Driving Performance and Security of Ultimate Eco Cars, FCVs

Japan has led the world in developing the production model of Fuel Cell Vehicles (FCVs), heralding the hydrogen energy society.
FCV is called an ultimate eco-car which is an electronic vehicle generated by a chemical reaction between oxygen in the atmosphere and hydrogen, and it does not emit any CO2.
However, hydrogen is flammable and becomes explosive when its concentration exceeds 4%. Automobile safety should support safe driving practices on public roads.
NGK SPARK PLUG CO., LTD. succeeded to further develop hydrogen leak detection sensors for FCVs which can detect even minute amounts of hydrogen. NGK SPARK PLUG CO., LTD. plans to start mass production of sensors. Here, we would like to identify the project member's challenges they took in order to start mass production.

Ichikawa:A member of the project management group. He is the only member who has worked on the hydrogen leak detection sensors since the start of their development. He has sufficient knowledge from development to manufacturing.

Igawa:He has been involved in the development of MEMS since 1998. In this project, he is in charge of development of sensor elements.

Suzuki:He has worked on the project for 3 years. He is engaged in the development of electronic circuits.

The industry's first sensor for automobiles was a challenge of the impossibility.

It is difficult for people to keep being motivated when they cannot achieve their goals. But if people continue their effort, they will be able to achieve their goal.

In 2000, automotive industry started the development of fuel-cell vehicles, "FCVs." NGK SPARK PLUG CO., LTD. joined the development of hydrogen leak detection sensors. Our company has already implemented sensor technologies including oxygen sensors for automobile and has been working on further developments.

When the company began negotiations with their clients, automobile manufacturers, it created a team work that included Ichikawa who had worked on technological developments related to hydrogen for over 10 years, Igawa, a specialist of elements; and Suzuki, a circuit designer.

There were various regulations concerning the safety of FCVs which use hydrogen fuel, therefore, their sensors have to meet stringent requirements such as detection accuracy and durability.
"How can we develop exclusive and superior detection sensors?"
First of all, members were really focused on a particular sensor method. <Catalytic combustion method> with direct combustion of detected hydrogen gas was technically easy to use and highly accurate. But it hastens the deterioration and has durability problem. Although they had technical difficulties, they chose to use the <thermal conductive method> which has more efficient durability by utilizing warmed heaters. If they can complete the sensor, it will be the industry's first in-vehicle sensor.

The decision was based on the conviction, "We should make the product which is valuable for customers and not easy to make." But this brought them a challenge which was harder than anticipated.

Atomic-level Studies for Developing Advanced New Technologies

<Thermal conductive method> sensor uses hydrogen property whose thermal conductivity is specifically higher than other types of gases. Hydrogen absorbs heat more than other gases do, when its temperature is kept constant by a constant power electrical source. The heater needs more electricity to maintain a specific temperature, so hydrogen concentration becomes proportional to the required power.

The first challenge was identifying an element that can detect the subtle change.

Crystals of elements could have small holes and damages. Igawa knew about the defects by reading articles, but it was the very first time for him to observe real defects by using transmission electron microscope.
The most difficult part was that holes and damages increased electrical resistance values. Therefore, when heat is generated by power distribution, defects are repaired and aligned, then electrical resistance decreases. If this influences the property, elements are unusable.
Igawa states "We should create well-regulated and perfect crystals of elements to prevent deformation." Igawa understood the problem by detecting each atomic disorder, and found the method to remove the defect. Then he created the elements that could be used for sensors.

This element is manufactured by MEMS (Micro Electro Mechanical Systems), our own technology. Its size is only 3mm × 2.5mm with minimal level electrical power required to operate. It is an integration of both mechanical and electronic technologies.
Igawa was a specialist who had engaged in development of MEMS since its technology started. By utilizing the technology, he could create a ceramic package with small MEMS elements for automobiles. This success has led the team to the development of its own electronic circuits.

Is it possible to detect microvolt levels of problems?
—Difficulties in circuit design.

Hydrogen leak detection sensors of automobiles can detect microvolt (millionth part of a volt) though typical sensors detect 1/1,000 volt. In the industry, it was commonly known that especially thermal conductive method sensors hardly detect small amounts of voltage.
"It is technically impossible——."
Ichikawa and his colleagues had hard talks and sometimes they were about getting into arguments, but Ichikawa kept saying, "Theoretical values showed possibilities. So it must be possible." Automobile manufacturer asked us to develop the sensor because of their high expectations for our sensors and ceramic technology, which was established over many years of partnership. Though there was no guarantee that the product would be adopted, the team combined the skills and unified the efforts of all members in order to meet client's high expectations.

The team began the development of electronic circuits which can detect small microvolt. When sensors are situated in the vehicle engine rooms, they become sensitive to electrical and magnetic noise, which are the obstacles of reading small electrical signals.
They prepared a special measuring instrument that can detect hydrogen of 4% or less, but they encountered a number of problems such as air stream of an air conditioners, room temperature and operational influence of personal computers interrupting stable measurement of weak voltage. After much struggle, they identified a method to calculate quantity of hydrogen by changing temperatures of sensors and correcting for external influence by comparing the measurement values.

"Sensor should send signals only when hydrogen leaks. This is fundamental but it is the most important part." Suzuki continued to research with his team to find the solution for difficult issues that they faced, but each time they presented the sensor to automobile manufacture, they discovered new issues.

As a result of trial and error process, they finally completed the circuit design that could detect fine electrical currents. The design embodied our own technology that integrates both ceramic technology and electronics technology.

Light at the end of the tunnel. They believed themselves.

We could describe going through the process of this project as walking through a long tunnel that we could not see its end, rather than "climbing over the wall."

The shipping time was determined but there was no guarantee that the automobile manufacturer would select their sensor. Furthermore, the team needed to meet client's high level requirements: and to guarantee detection accuracy of 100 ppm with both a temperature of 100ºC and 100,000 km drive.
How did the development team members maintain their motivation in such challenging situation?

The primary factor that supported them was gaining the trust of client.
"To be honest, we almost gave up on the project. But even when we failed, our client was kindly patient and waited until we could solve the problems." Ichikawa remembered the moment.

Also Suzuki said, "Our client believed that we would not fail. So we came up to their expectations. Driven by the commitment to succeed, we tackled the next challenges."
Over a long period of time, we gained the trust through the quality of various products including sensors.

The other factor behind maintaining their motivation was their new spirit: to work on the development from the start to finish.
Despite the fact some developments of new product cannot be commercialized, this project had client's expectations and the shipping schedule was already decided. In addition, members could be involved with all the process from development to mass production. They were very passionate about their work throughout the process.

Suzuki remembered the days of first shipment.
The client gave the team encouraging words, "NGK SPARK PLUG CO., LTD. is the only company that can implement this technology."
"Yes! We can do this!" Client's trust ignited the team's passion and accelerated the project towards the ultimate goal.

Overcoming the challenges of mass production

When the team came close to the accomplishment, they faced a further issue.
When they actually manufactured the sensors, some sensors could not detect 100ppm. It took a long time to identify the cause because too many factors could fluctuate the voltage, but finally they achieved mass production by solving these problems step-by-step.

In addition, each manufactured sensor was slightly different in its performance. Each sensor's function was executed best by "matching," which adjusted sensors based on the measurement of properties against temperature and humidity before shipping. It was a problem that the matching included many processes, but they also improved the process to produce sensors fast and then to ensure its quality.

Throughout struggles so far, each member obtained large gains.
"I believe that we accumulated the know-how that we could apply to a wide range of fields. We also advanced our own technology," said Igawa.

Suzuki also said proudly, "We didn't only develop theory of circuit technology to measure weak voltage, but also implemented it with materials that we regularly didn't use. It was a great advantage for our company to complete the voltage detection sensor for automobile that can detect microvolt."

Igawa who managed the project had a sense of confidence stating "I appreciate the total integration of elements, circuits, and production departments. I also expanded relationships and ties with people and obtained new knowledge. This is the second sensor with MEMS, but this time we have created new sensors for next-generation automobiles."
It is very significant that we developed a new core technology by challenging new fields based on existing core technology of sensors and ceramics.

However we are well prepared to tackle future challenges.

FCVs need cost reduction for their wide spread. So we also need to reduce the cost of our sensors, even though it is a small part. It is possible that they need to reconsider the material and technologies, or they need to start over with a clean slate.
Is it possible for them to maintain their motivation?
"It's no problem. Our members are strong enough," Igawa laughed. Innovation in NGK SPARK PLUG CO., LTD. will continue to further challenges.