Simplified in-cylinder pressure sensor - htw saar
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Simplified in-cylinder pressure sensor using highly-sensitive chromium thin-films and direct contacting by laser welding D. Wachter 1 , D. Vollberg 2 , S. Schwebke 2 , G. Schultes 2 1 ZeMA gGmbH, D-66121 Saarbrücken; 2 HTW des Saarlandes, D-66117 Saarbrücken Literature & Sources Acknowledgments Contact E-Mail: [email protected], Phone: +49 681 - 85 787 - 63 We thank T. Heinze, H.-W. Groh and the automotive team at htw saar for the possibility to test our sensors on their engine test benches. This work was funded by the BMBF within FHprofUnt with the project number 13FH010PX5. Steel membranes were generously supplied by Kavlico Pressure Sensors. [1] Wikimedia commons, Clemens Ratte-Polle. CC BY-SA 4.0 [2] Strain sensitive chromium thin-film. Paper in preparation. [3] G. Schultes, D. Göttel, M. Cerino: Hochempfindliche Stahlmembran-Drucksensoren mit lasergerechtem Messbrückenlayout, 11. Dresdner Sensor-Symposium, 9.-11. Dez. 2013 • Glow-plug at diesel engine can be exchanged for sensor • Stainless-steel membrane as sensing element • Simple turned steel part as carrier body, no moving parts • Nominal pressure 250 bar • Direct contact between membrane and combustion chamber • Wheatstone bridge structured into chromium thin film[1] sputtered onto a SiO2 layer of insulation CAD rendering with partial section of pressure sensing element (red) at the front Schematic of sensor layout Magnified thin-film structure Sensing element ready for contacting Sensor concept High temperatures, vibrations and the need for high temporal resolution place special requirements on in-cylinder pressure sensors and on the electrical contacts of the sensor element. In combination with the given small geometry and the required low production costs, high reliability and long-term stability, this represents a special challenge. A chromium based thin-film and an experimental laser welding are tested without using moving parts. Closed loop control of the combustion process based on real-time measurement of in-cylinder pressures is a key technology for the reduction of emissions caused by combustion engines and the most efficient usage of fuels. [1] Motivation • Sensor concept looks promising Long-term evaluation in progress • Complete sensor package prototype including smart electronics in development Goal of the “Smart Combustion” FHprofUnt project • Laser contacting will be explored in more detail in the future Interesting as no additional Material is used. Automation possible? • Chromium thin-film has shown interesting behaviour Paper[2] in preparation Conclusions & Outlook Thermal Temperature range ok for thin-film and contacting method? Mechanical Thin-film properties & membrane geometry dictate layout design • Circular pressure membrane Strain zone in center (R = 0) Compression zone at outer edge • Thin-film has a very high transverse sensitivity of 90% High contribution of tension zone Low contribution of compr. zone Modelling & Simulation Expected dynamic temperature gradient over one cycle Expected ‘effective strains’ for radially resp. tangentially arranged measuring resistors • Constant gradient in bridge shifts zero point, but easy to compensate High pass Recalibration between cycles • In-cycle gradient change is hard to compensate Temperature insensitive thin-film • Laser contacting and prototypes reliable so far with >200 h of testing • Improvement of signal quality likely by tweaking thin-film process parameter • Experimental laser welding used on all electrical contacts • Additional nickel-based 150 nm thin film deposited on deformation-neutral zones allows for soldering or welding • 150 μm wire coated with insulating material welded onto 210 nm thin film layer • Tip of wire pre-melted by single laser shot to form a ball of 500 μm diameter • Second shot causes wire and thin-film to fuse Tight joint without destroying insulation layer, typically resisting 4 N shear force Contacted sensing element with one wire per contact pad Welding sample analysis on a SEM. Blue: Wire doesn’t fuse with chromium thin-film. Orange: Reflection damaged thin-film, insulation ok. Contacting by laser welding Steel Insulation layer, 5 μm Chromium thin-film, 60 nm Nickel-based thin-film, 150 nm • 5 pressure sensors with variations and 1 temperature sensor Predictions verified by test results High sensitivities above 20 mV/V Promising first results • Temperatures up to 200 °C at sensing element, depending on coolant temperature and engine load Exemplary pressure signal over one engine cycle, double peak from pre-injection visible Dynamic temperature gradient over 3 engine cycles, likely source of thermal shock Results
Transcript of Simplified in-cylinder pressure sensor - htw saar
Simplified in-cylinder pressure sensorusing highly-sensitive chromium thin-films and direct contacting by laser welding
D. Wachter1, D. Vollberg
2, S. Schwebke
2, G. Schultes
2
1 ZeMA gGmbH, D-66121 Saarbrücken; 2 HTW des Saarlandes, D-66117 Saarbrücken
Literature & Sources Acknowledgments
ContactE-Mail: [email protected], Phone: +49 681 - 85 787 - 63
We thank T. Heinze, H.-W. Groh and the automotive team at htw saar for the possibility to test our sensors on
their engine test benches.
This work was funded by the BMBF within FHprofUnt with the project number 13FH010PX5.
Steel membranes were generously supplied by Kavlico Pressure Sensors.
[1] Wikimedia commons, Clemens Ratte-Polle. CC BY-SA 4.0
[2] Strain sensitive chromium thin-film. Paper in preparation.
[3] G. Schultes, D. Göttel, M. Cerino: Hochempfindliche Stahlmembran-Drucksensoren mit
lasergerechtem Messbrückenlayout, 11. Dresdner Sensor-Symposium, 9.-11. Dez. 2013
• Glow-plug at diesel engine can be
exchanged for sensor
• Stainless-steel membrane as
sensing element
• Simple turned steel part as carrier
body, no moving parts
• Nominal pressure 250 bar
• Direct contact between membrane
and combustion chamber
• Wheatstone bridge structured into
chromium thin film[1] sputtered onto a
SiO2 layer of insulation
CAD rendering with partial section of pressure sensing
element (red) at the front
Schematic of sensor layout Magnified thin-film structureSensing element ready for contacting
Sensor concept
High temperatures, vibrations and the need for high temporal resolution place
special requirements on in-cylinder pressure sensors and on the electrical contacts
of the sensor element. In combination with the given small geometry and the
required low production costs, high reliability and long-term stability, this represents
a special challenge. A chromium based thin-film and an experimental laser welding
are tested without using moving parts.
Closed loop control of the combustion process based on real-time
measurement of in-cylinder pressures is a key technology for the
reduction of emissions caused by combustion engines and the
most efficient usage of fuels. [1]
Motivation
• Sensor concept looks promising
Long-term evaluation in progress
• Complete sensor package prototype including smart electronics in development
Goal of the “Smart Combustion” FHprofUnt project
• Laser contacting will be explored in more detail in the future
Interesting as no additional Material is used. Automation possible?
• Chromium thin-film has shown interesting behaviour
Paper[2] in preparation
Conclusions & Outlook
Thermal
Temperature range ok
for thin-film and
contacting method?
Mechanical
Thin-film properties &
membrane geometry
dictate layout design
• Circular pressure membrane
Strain zone in center (R = 0)
Compression zone at outer edge
• Thin-film has a very high transverse
sensitivity of 90%
High contribution of tension zone
Low contribution of compr. zone
Modelling & Simulation
Expected dynamic temperature gradient
over one cycle
Expected ‘effective strains’ for radially resp.
tangentially arranged measuring resistors
• Constant gradient in bridge shifts zero
point, but easy to compensate
High pass
Recalibration between cycles
• In-cycle gradient change is hard to
compensate
Temperature insensitive thin-film
• Laser contacting and prototypes reliable so far with >200 h of testing
• Improvement of signal quality likely by tweaking thin-film process parameter
• Experimental laser welding used on all electrical contacts
• Additional nickel-based 150 nm thin film deposited on deformation-neutral zones
allows for soldering or welding
• 150 μm wire coated with insulating material welded onto 210 nm thin film layer
• Tip of wire pre-melted by single laser shot to form a ball of 500 µm diameter
• Second shot causes wire and thin-film to fuse
Tight joint without destroying insulation layer, typically resisting 4 N shear force
Contacted sensing element with one
wire per contact pad
Welding sample analysis on a SEM.
Blue: Wire doesn’t fuse with chromium thin-film.
Orange: Reflection damaged thin-film, insulation ok.
Contacting by laser welding
Steel
Insulation layer, 5 µm Chromium thin-film, 60 nm
Nickel-based thin-film, 150 nm
• 5 pressure sensors with variations
and 1 temperature sensor
Predictions verified by test results
High sensitivities above 20 mV/V
Promising first results
• Temperatures up to 200 °C at
sensing element, depending on
coolant temperature and engine load
Exemplary pressure signal over one engine cycle,
double peak from pre-injection visible
Dynamic temperature gradient over 3 engine cycles,
likely source of thermal shock
Results
