Cycle
Resolved, In-Cylinder Friction Measurement Technique Development
Abstract:
A large portion of engine friction is developed at the piston/ring
assembly and cylinder liner interface. Friction measurement
at this interface is extremely difficult, but the knowledge
of its relative values is very important for producing lower
friction engines. Hence, the Instantaneous IMEP (Indicated Mean
Effective Pressure) method has been developed. There are many
challenges with this technique, most notably measuring the force
on the connecting rod. Several techniques to measure this force
are being investigated, the best of which is an inductively
powered, wireless microwave transmitter.
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| Background:
The
technique used to measure cycle resolved, in-cylinder friction
is commonly referred to as the Instantaneous IMEP technique. By
doing an instantaneous force
balance in-cylinder friction can be calculated on a crank
angle basis. The key to this technique is the ability to measure
the force transmitted to the connecting rod which requires precision
installation of strain gauges and a means to power (since strain
gauges are passive transducers) and acquire the signal from the
strain gauges. In the past a mechanical
linkage (typically called a grasshopper linkage) was used
to support and protect power and signal wires that ran from the
bottom end of the connecting rod, into a modified oil pan, and
out the engine. These wires are connected to the strain gauge
on the connecting rod on one end and to a signal amplifier and
conditioner on the other. There are several draw backs to this
technique including speed limitations and dynamic considerations
for the linkage, wire fatigue failure, and the necessity of engine
modifications which may change engine characteristics. Because
of the shortcomings of the grasshopper linkage a wireless telemetry
system is being developed.
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Motivation:
Friction between the cylinder walls and the piston/ring pack assembly
constitutes a very large portion of total engine frictional losses
(30 to 50 percent). In an era where fuel conservation is becoming
increasingly important, reduction in mechanical friction is an
outstanding way to increase fuel economy without sacrificing performance.
With this tool, friction due to the interface between the piston/ring
assembly and the cylinder wall can be directly studied.
Researchers:
Stani Bohac
Dennis Assanis
Kulasegaram “Guga” Gugaratshan (Dana Corp.)
Kimm Karrip (Dana Corp.)
Sponsors:
Automotive Research Center (U.S. Army TACOM)
General Motors
Dana Corporation |
Results and Contributions:
The wireless, inductively powered, microwave transmission
system that acquires the signal from the strain gauge on the
connecting rod has been calibrated.
Several preliminary tests have been run in the development of
this system which revealed what is believed to be interference
from the inductive coupling which transfers power from the power
supply to the capacitors in the transmitter. Unsuccessful attempts
where made to measure this interference as well as to help shield
the inductive effects. Because of this a wireless, battery powered,
microwave transmission system is currently being developed. In
parallel the grasshopper linkage is being revived to provide validation
of wireless telemetry system.
The tool is being used to measure design, tribological and other effects
on in-cylinder, instantaneous friction in support of other research projects, as well as being used to calibrate computer models.
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