Piston displacement measured in real time01 October 2006
A UK-based automotive consultancy is using miniature eddy current displacement sensors built into gasoline engine pistons to measure the displacement between the piston and the cylinder bore in real time. This means engineers can look closely at how the piston moves with critical engine operating parameters, such as cylinder pressure and engine speed.
The technique results from an internal research project at Mahle Powertrain, formerly Cosworth Technology, part of Mahle Group, the supplier of engine components and systems.
The internal research project allowed engineers to view the movement throughout the complete combustion cycle. Two Micro-Epsilon UO5 eddy current displacement sensors were used for the project, due to their high precision in extreme environments and sub-miniature design (2mm diameter by 4mm in length with a 0.5mm diameter sensor cable).
Because of the piston design, the ‘UO5’ sensors needed to be positioned as high and as low as possible on the piston. In this case, the uppermost sensor was mounted between the first and second piston ring on the thrust face. The other sensor was vertically aligned, as low as possible on the piston skirt.
As Carl Godden, senior development engineer at Mahle Powertrain, explained: “The position of the sensors enabled the measurement of any ‘rocking’ movements on the gudgeon pin as it travelled up and down the bore. Effects of varying the cylinder pressure, engine speed, piston squirt jet flow and other potentially influential parameters could then be viewed in real time.”
Mahle Powertrain utilised its own mechanical linkage mechanism. This enabled cables to be routed from the piston area, down the connecting rod, across two pivoted beams and out via the sump.
The system can be utilised in both gasoline and diesel engine applications. Its ability to give real time data via hard wiring, means data acquisition resolution is only limited by the maximum speed of the amplifiers or the acquisition system.
MAHLE Powertrain Ltd
Micro-Epsilon Messtechnik GmbH
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