Crank Angle BAsed Virtual Cylinder Pressure Sensor in Heavy-Duty Engine Application
The in-cylinder pressure is an important signal that gives information
about the combustion process. To further improve engine performance,
this information can be used as a feedback signal in a control
system. Usually a pressure sensor is mounted in the cylinder to
extract this information. A drawback with pressure sensors is that
they are expensive and have issues with aging. This master’s thesis
investigates the possibility to create a virtual sensor to estimate
in-cylinder pressure based on crank angle degree sensor (CAD-sensor)
data and physical models of the heavy-duty engine.
Instead of using the standard mounted CAD-sensor an optical
high-precision sensor mea- sures the elapsed time between equidistant
angles. Based on this signal the instantaneous angular acceleration
was estimated. Together with the inertia of the crankshaft, connecting
rods and pistons, an estimation of the engine torque was
calculated. To be able to extract in- cylinder pressure from the
estimated torque, knowledge about how the in-cylinder pressure signal
propagates in the drivetrain to accelerate the flywheel needs to be
known. Two engine models based on the torque balance on the crankshaft
are presented. The fundamental dif- ference between them is how the
crankshaft is modeled, rigid body or spring-mass-damper system. The
latter captures torsional effects of the crankshaft. Comparisons
between the estimated torque from sensor data and the two engine
models are presented. It is found that torsional effects of the
crankshaft is present at normal engine speeds and has a significant
influence on the flywheel torque.
A separation of the gas torque contribution from one cylinder is done
with CAD-sensor data together with the rigid body engine model. The
in-cylinder pressure is then estimated by using the inverse
crank-slider function and a Kalman filter estimator. The estimated
pressure captures part of the compression and most of the expansion at
engine speeds below 1200 RPM. Due to the crank-slider geometry the
pressure signal disappears at TDC. The torsional effects perturb the
estimated pressure during the gas exchange cycle.
Further development must be made if this method is to be used on
heavy-duty applications in the future.
Mikael Gustafsson
2015
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Senast uppdaterad: 2021-11-10
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