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Release: June 11, 2008
NGK Insulators, Ltd.

Bringing the world's first high-precision NOx sensor to market

NGK (President and CEO: Shun Matsushita; Head office: Nagoya), jointly with its cooperation partner Continental, has brought to market the world's first in-vehicle high-precision NOx sensor, achieving a 30% reduction in NOx measurement errors from previous models. This NOx sensor is both company's response to a worldwide tightening of diesel exhaust gas regulations. In order to ensure a stable supply of these sensors, NGK will increase its annual production capacity to two million units in 2009.

The only mass-production manufacturer of in-vehicle NOx sensors in the world, NGK has utilized its proprietary, patented technologies to develop a high-precision NOx sensor with a 30% measurement error reduction, from the ±15 ppm NOx detection accuracy measurement error rate of earlier products to the current ±10 ppm, as well as favorable results with regard to durability evaluation.By joining forces with Continental, both companies together have has succeeded in bringing to market the world's first in-vehicle NOx sensor that is capable of complying with strict exhaust gas regulations such as the United States' US10 emission standard. Orders from major US companies have already been received, and NGK/Continental are being approached by many other companies worldwide.

NGK currently operates production lines with an annual production capacity of one million NOx sensors at the company's Komaki Plant (located in Komaki, Aichi Prefecture) and Nagoya Plant (located in Mizuho, Nagoya) and has been supplying these sensors, via Continental, to automobile manufacturers in Europe and other areas. Now that NGK together with Continental have has succeeded in bringing a high-precision NOx sensor to market, NGK expects to see a rapid expansion in demand and has therefore at this time decided to invest approximately 1.2 billion yen to increase the capacity of its existing production lines. The expanded lines will begin operation in July 2009, increasing annual sensor production capacity to two million units. The prompt establishment of a mass-production system to meet the anticipated increase in demand will establish NGK together with Continental as the worldwide leaders in the field of NOx sensors.

Automobile exhaust gas regulations have recently been strengthened worldwide. With regard to diesel vehicles in particular, the regulations for nitrogen oxide (NOx) emissions, in addition to particulate matter (PM) emissions, are being further strengthened. Regulations such as the United States' US10 emission standard, the European Euro V regulations and Japan's post new long-term (exhaust gas emission) regulations will take effect starting in 2010 (See Fig. 1). Therefore, a high-precision NOx sensor that can detect the NOx density in exhaust gas with a higher measurement precision than has been available to date will be required for optimum control of the performance of the exhaust gas purifiers for diesel engines and for the failure diagnosis of these purifiers.

The in-vehicle NOx sensor mounted in an automobile's exhaust pipe detects the NOx density in the exhaust gas, and is used for the control of the exhaust gas purifier and for diagnosis of its failure (Fig. 2). As exhaust gas regulations become further strengthened in the future, this component will become indispensable for the reduction of NOx gas in diesel vehicles. Formerly, oxygen sensors utilizing zirconia ceramic (ZrO2, Fig. 3) were used to detect the amount of oxygen ions in the exhaust gas, and that amount was used as a basis for the calculation of NOx density. However, because exhaust gas contains both oxides and oxygen (O2) in addition to NOx, it was difficult to precisely detect only the oxygen ions that originated from NOx. In order to comply with regulations that will become further strengthened in the future, a more high-precision and more durable NOx sensor capable of detecting low-density NOx even in the high-temperature, severe operating conditions of an automobile exhaust gas pipe and of maintaining performance over a long period of time was sought. NGK made full use of the ceramics technology that it had cultivated to date, and by forming ZrO2 into a proprietary two-chamber shape and using a multi-layered element, developed a sensor to detect with high precision only those oxygen ions originating from nitric monoxide (NO) from among the oxygen ions present in the exhaust gas. The company has obtained a basic patent relating to this proprietary element (Fig. 4).

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< Glossary and Diagrams >

Fig. 1: Exhaust gas regulations for diesel vehicles in Japan, the United States, and Europe

Exhaust gas regulations for diesel vehicles have become increasingly rigorous over the past few years, and regulations for PM and NOx emissions are expected to be further strengthened.

Exhaust gas regulations for diesel vehicles in Japan, the United States, and Europe Exhaust gas regulations for diesel vehicles in Japan, the United States, and Europe (trucks and buses)

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Fig. 2: In-vehicle NOx sensor usage example

The sensor is mounted behind the exhaust gas purifier. The performance of the exhaust gas purifier is monitored by feeding back detected NOx values to the ECU.

 In-vehicle NOx sensor usage example

Fig. 3 Zirconia ceramic (ZrO2)

This type of ceramic is an oxide of zirconium (Zr), one of the rare earth metals. An important property of this ceramic is that it conducts oxygen ions when voltage is applied at high temperatures. Conversely, an electric current is generated when oxygen ions are mobile. This property can be put to practical use when zirconia is used in oxygen pumps and oxygen sensors and in fuel cell electrodes.

Zirconia ceramic (ZrO2)

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Fig. 4 Schematic diagram of automobile exhaust gas and in-vehicle NOx sensor (element)

In addition to NOx, other elements such as carbon monoxide (CO), carbon dioxide (CO2), water (H2O) and oxygen (O2) are present in automobile exhaust gas. NGK's high-precision NOx sensor elements are divided into two chambers. Chamber 1 removes all oxygen ions in the automobile exhaust gas except for those generated by nitric monoxide. Chamber 2 detects only oxygen ions originating from nitric monoxide (The company has obtained a basic patent for this proprietary element).

NGK Insulators, Ltd. Basic principle of the high-precision NOx sensor

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< Attachment >Photograph of in-vehicle high-precision NOx sensor (Smart NOx-Sensor)

Photograph of in-vehicle high-precision NOx sensor (Smart NOx-Sensor)

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