Micro-Epsilon - PRODUCT NEWS
Sensors enable real time measurement of engine piston displacement.
A UK-based automotive consultancy is using miniature, eddy current
displacement sensors built into pistons on gasoline engines, 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
Mahle Powertrain Ltd, formerly Cosworth Technology, is an automotive consultancy based in Northampton. The company is part of Mahle Group, a leading supplier of
piston systems, cylinder components, valve train systems and air and liquid
management systems to the automotive industry.
One of Mahle Powertrain's recent internal research projects involved the use of Micro-Epsilon sensors to measure the displacement between the piston and the
cylinder bore on a gasoline engine. The sensors were mounted within the piston
itself, so that movement could be viewed throughout the complete combustion
cycle. Mahle has worked successfully with Micro-Epsilon for a number of years
and so when this complex project emerged, Mahle consulted with Micro-Epsilon
for its expert advice.
Two objectives of automotive engine development are
to minimise harmful emissions and to reduce oil
consumption. To obtain reliable measurements, which
can then be used to help develop the engine and
components for high volume production, tests need to
be conducted on real engines and under realistic
At Mahle Powertrain, the test environment was harsh and so selection of the sensor
was critical. 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 explains: "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."
To carry out these measurements, Mahle Powertrain utilised its own mechanical
linkage mechanism. This enabled cables to be routed from the piston area, down
the connecting rod, and across two, pivoted beams and out via the sump. This
system enabled Mahle engineers to acquire a diverse range of measurements
from a wide range of miniature transducers.
Mahle's linkage 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. In this particular application, the output of the Micro-Epsilon 'U05' sensors was plotted against crank angle by using a high resolution crank angle encoder.
According to Godden, the UO5 sensor's miniature, 0.5mm coaxial cable "proved more than durable for the duration of
the tests, even under such an extreme environment". Mahle Powertrain's test schedule meant that the U05 sensors were subjected to sustained speeds of up to 6,500 rpm with a
total test duration of 35 hours, with oil temperatures reaching well over 100°C.
The sensor has a high temporal resolution (0.1° per crankshaft rotation) and a very
high spatial resolution (~ 1µm) and is not affected by fuel, oil, exhaust fumes or other contaminants.
Micro-Epsilon (www.micro-epsilon.co.uk) is a major global manufacturer of sensors, headquartered in Germany. The company's range of sensors measure everything from displacement to distance, position, vibration, dimensions and thickness, using both contact and non-contact measurement techniques. These techniques include inductive, differential transformer, eddy-current, capacitive, laser-optical, potentiometric and draw-wire principles.
With more than 30 years' experience in the industry, Micro-Epsilon isn't just a sensor manufacturer. The company is highly innovative and understands the importance of providing complete solutions and support services for its customers. The firm is renowned for its expertise in consulting, development and application of industrial sensors to complex, customer-specific solutions for measurement, inspection and automation. The focus is on selling technical advantage to its clients.
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