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Abstract |
Determining TDC Position using Symmetry and other Methods
It is important to determine the phasing of a measured cylinder
pressure trace
and crank angle with high accuracy. The reason is that erroneous
determination of the position of TDC is a major error source when
calculating properties such as heat release etc.
A common way to determine the TDC position is to study motored
cycles. Heat transfer makes the task more complicated, since it shifts
the position of the maximum pressure away from TDC. In this paper a new method for determining the TDC position is
proposed that does not require any additional sensors other than a
cylinder pressure sensor and an incremental encoder. The idea is to
find a point that the cylinder pressure from a motored cycle is
symmetric around, since the volume is close to symmetric on either
side of TDC.
The new method and four published methods are tested and evaluated.
Cylinder pressure data used for comparison are from simulations
of a SAAB Variable Compression engine. The investigation
shows that the methods have an error that is in the range of
0.1 crank angles or less, but are sensitive to errors
in geometry and heat transfer information. The symmetry method is less
sensitive to these errors than most of the other methods, and
is not affected by an offset or gain error in the cylinder
pressure signal. It is also the least sensitive method with respect to
noise.
Ylva Nilsson and Lars Eriksson
SAE Technical paper series SP-1830, 2004
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