March 2018

Pressure sensors

Media-resistant pressure sensors for aggressive fuel line environments

The continuous reduction of fuel consumption and vapor emissions is driving the roadmap of carmakers and their suppliers. Combustion engines are at the center of attention for ever stringent environmental regulation around the world. Based on an innovative sensor platform for high accuracy pressure sensing applications, TDK has developed new robust fuel pressure sensors that are resistant to the growing number of fuels and help carmakers to conform with new emission legislation.

Pressure sensors able to operate accurately over a long service life when in contact with aggressive media are a prerequisite for reliable and in many cases mandatory on-board diagnostics and control systems in vehicles. In many of today’s pressure sensor solutions, elastomer materials are used for the interconnection of the sensing element and its package and come into contact with the media. However the interaction of fuels and soft glues (elastomers) is a known weakness for accurate measurements and long-term stability, especially considering the growing variety of fuels, mixtures and additives used worldwide.


Advanced pressure sensing technology enables reliable and accurate measurement

TDK’s innovative tank pressure sensor design takes a different approach: All plastics and elastomers that come into direct contact with fuels are replaced with extremely durable glass-based materials that are matched in terms of thermal expansion (Figure 1). Unlike elastomers, these materials do not swell, shrink or become brittle, thus eliminating inaccurate pressure measurements due to signal drift or leakage. 

 

Figure 1: The advanced pressure sensor platform for fuel line and tank applications eliminates swelling of materials and interconnections and enables flexible integration in applications with temperatures up to 125 °C. All plastics and elastomers that come into contact with fuel are replaced with durable CTE-matched materials.


As a consequence, this sensor technology offers a high resistance against all fuels and provides an accurate signal with a narrow tolerance of less than ±1% FS over a wide temperature range of -40 °C to +125 °C, even at temperature changes within a certain time period. TDK’s pressure sensor technology thus represents an advanced sensor platform for multiple fuel applications and enables a wide variety of application-specific options for housings and connectors.


Long-term signal stability and highest media resistance

Based on its pressure sensor platform, TDK has developed an innovative tank pressure sensor that – especially in hybrid vehicles – satisfies the demands for optimized leakage controls and further pushes the limits of sensing accuracy (Figure 2).

 

Figure 2: In addition to long-term signal stability and highest media resistance over lifetime, the new tank pressure sensor offers a high relative accuracy of just 0.2%.


Evaporation emissions control systems are designed to prevent fuel vapor from being discharged into the atmosphere. Pressure sensors monitor the tank pressure either during electrical driving mode or when the vehicle is resting and must be able to detect very small pressure and temperature deviations. With an improved calibration concept, which was developed specifically for the leakage control algorithm, TDK has further improved the relative pressure sensing accuracy down to 0.2%.

The new sensor offers gauge pressure measurement over a wide range, for hybrid vehicles typically from -100 mbar to 350 mbar. It is equipped with a digital interface (SENT) for on-board diagnostics and additional temperature sensing. Based on TDK’s robust pressure sensing platform, the sensor provides long-term signal stability and highest media resistance over lifetime.

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