An Investigation of Maximum Brake Torque Timing based on Ionization Current Feedback
Abstract
For every operating condition of an internal combustion engine there exists an optimal spark timing, called
maximum brake torque (MBT), which maximises the output torque and the efficiency of the engine. Traditionally
MBT timing is implemented as an open-loop control where the ignition timing is found by using a combination of
static lookup tables and sensor information. With a direct closed-loop control from the combustion process the
performance of internal combustion engines could be improved. The thesis investigates if it is possible to
estimate the MBT timing from the ionization current for every operating condition of a spark ignited engine
where the operating conditions are defined by the engine parameters lambda, internal exhaust gas recirculation,
engine load, engine speed and spark advance.
First an investigation of how much loss of torque an error from the MBT position corresponds to is made. Then
the influence of the engine parameters on the shape of the ionization current was studied. Last different peak
pressure position (PPP) estimating algorithms are presented and a new technique is developed where an engine
operating point dependant part of the ionization current is used depending on the current operating condition
of the engine. Two of the presented PPP estimating algorithms are then complemented with this technique and the
results look promising.
Janek Magnusson
2007
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