Special Features 2014

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Special Features SHINKA-1

Delving of Automobile Oxygen Sensors

Helping Prevent Atmospheric Pollution by Controlling the Exhaust Gas Cleaning Performance of the Three-way Catalyst*
* An exhaust gas cleaning device that simultaneously eliminates carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx)
in exhaust gas through oxidation or reduction.

History of Oxygen Sensors

Voice of our Developer

Aiming to establish new elemental technologies

The precious metal platinum is needed to make the elements in oxygen sensors perform their function, but it is an extremely expensive metal, which is a factor in pushing up the cost of sensors. We go to a lot of trouble to identify the minimum amount of platinum required to strike a balance between guaranteeing the functional aspect of the sensor with cost reductions. Oxygen sensors still have a short history relative to the history of the internal combustion engine, and that is why there is still unexplored territory in terms of methods of usage and development goals. We will work to establish elemental technologies in order to handle new areas.

Sensor Engineering Dept.II, Sensor Division, Automotive Components Group
Uematsu

Control of Exhaust Gas Cleaning Performance

* The mixing ratio of air (oxygen) and fuel in an engine. The air-fuel ratio for the complete combustion of fuel in exhaust gas (the cleanest) is called the stoichiometric air-fuel ratio.

Preventing Atmospheric Pollution

Oxygen sensors need to function in the shortest possible time after the engine starts. The activation time for NGK SPARK PLUG CO., LTD.’s late-model sensors is a mere five seconds. They also meet exhaust gas regulations becoming stricter around the world.

Stricter Automotive Exhaust Gas Regulations Advancing Worldwide

Automotive exhaust gas regulations have been strengthened worldwide from the perspective of environmental conservation, and exhaust gas regulations have been progressively introduced in emerging countries as well following developed countries such as Japan, the United States and Europe.
In particular, for diesel vehicles, regulations on NOx emissions have become stricter in addition to particulate matter (PM), and exhaust gas regulations are scheduled to be strengthened not only for passenger vehicles and trucks but also for off-road vehicles, including construction and agricultural machinery.

Automotive Exhaust Gas Regulations Worldwide

*1 Post new long-term: Automotive exhaust gas regulations established by Japan’s Ministry of Land, Infrastructure, Transport and Tourism (MILT) in order to further reduce PM and NOx emissions from newly sold trucks, buses and passenger cars.
*2 Tier 2/Bin#8, etc.: Exhaust gas regulations under the jurisdiction of the Environmental Protection Agency (EPA) under the direct control of the federal government of the United States. NOx regulatory values have been graded in all 11 Bins (Bin 1 – Bin 11).
*3 Euro 5, etc.: Exhaust gas regulations introduced in September 2009 and applied to sports utility vehicles (SUVs) and compact commercial vehicles in January 2011.

Oxygen Sensors Making Exhaust Gas Cleaning Systems Function Effectively

The three-way catalyst is the device that plays the primary role in cleaning exhaust gas from automobiles (gasoline vehicles). The three-way catalyst simultaneously eliminates the three major hazardous substances (CO, HC and NOx) contained in exhaust gas through oxidation and reduction. As such, the proper balance between the volumes of carbon, hydrogen and oxygen in exhaust gas is required for this process to be carried out successfully.
This balance is termed the stoichiometric air fuel ratio, which is also the condition for the complete combustion of the fuel by air (oxygen).
Oxygen sensors play a key role in the process. Oxygen sensors constantly keep the air-fuel ratio in the region close to the stoichiometric air-fuel point by detecting the concentration of oxygen in exhaust gas and feeding the signal data back to the engine control unit (ECU), allowing the three-way catalyst to perform its function fully.

Efficiency of catalytic converter

Significantly Reducing Activation Time in Step with Strengthening of Exhaust Gas Regulations

Since utilizing its specialist ceramics technology to develop zirconia oxygen sensors in the 1980s, NGK SPARK PLUG CO., LTD. has continually evolved products that meet more stringent exhaust gas regulations.

For an oxygen sensor to function, the sensor element needs to be activated by raising it to a certain temperature (300℃). As early oxygen sensors used the heat of the exhaust gas for this, they took several minutes to activate after the engine was started. However, it is necessary to activate the element as quickly as possible to meet stringent exhaust gas regulations. Therefore, in the second half of the 1980s, NGK SPARK PLUG CO., LTD. developed the zirconia oxygen sensor that activated in about 20 seconds using its own heat from a built-in heater in the sensor. Subsequently, we have shortened the activation time by improving the heater structure and the element, achieving activation in a mere five seconds after the engine starts for the latest model.

Developing Wide Range Oxygen Sensors that are also Useable with Diesel Vehicles

While evolving zirconia oxygen sensors, NGK SPARK PLUG CO., LTD. developed wide range oxygen sensors in 1980s that sense using a completely different and unique mechanism.

While a zirconia oxygen sensor only determines oxygen volume in the region close to the stoichiometric air-fuel ratio, a wide range oxygen sensor enables highly precise detection of oxygen concentration across a wide range by measuring the magnitude of deviation from the stoichiometric point. As a result, in addition to enabling more precise control of the air-fuel ratio, it was also applicable to diesel vehicles, in which the air-fuel ratio could not previously be controlled using an oxygen sensor.

In light of the worldwide strengthening of exhaust gas regulations in the 2000s. NGK SPARK PLUG CO., LTD. also made improvements to its wide range oxygen sensors, developing a product with the activation time reduced to five seconds through integration of the heater and element. NGK SPARK PLUG CO., LTD. is contributing to even cleaner exhaust gas.

Histogram of controlled A/F during driving mode

Supplying NOx Sensors to Meet Stringent NOx Regulations

Highly precise control of NOx is needed to meet the stringent NOx regulatory values of recent years.
NOx sensors measure the concentrations of NOx and oxygen in exhaust gas in real time, contributing to energy conservation and clean air by controlling NOx in gasoline direct injection engines and diesel engines.

*Position and job title are as of fiscal year 2014.