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Abstract |
Intake Air Dynamics on a Turbocharged SI-Engine with Wastegate
On turbocharged spark-ignited (SI) engines with wastegate the
position of the wastegate changes the exhaust manifold pressure. A
secondary effect of this is that the residual gas mass trapped inside
the cylinder at exhaust valve closing changes and causes the
volumetric efficiency to change. The volumetric efficiency is used to
estimate air-mass-to-cylinder which is important for good air/fuel
ratio control. Air-mass to-cylinder is not directly measurable so observers for
air-mass flow to the cylinder are therefore often proposed. For
observers with one state for intake manifold pressure and proportional
feed-back from measured state, there is a tradeoff whether to estimate
intake manifold pressure or air-mass-to-cylinder. A new nonlinear
air-mass-to-cylinder observer is suggested with two states: one for
intake manifold pressure and one for the in-cylinder air-mass offset
compared to expected using the volumetric efficiency. The exhaust manifold pressure can change rapidly in an engine with wastegate.
A method to estimate the exhaust manifold pressure is presented for diagnosis of
wastegate and turbocharger on SI-engines. It does not use any extra sensors in
the exhaust system after the calibration. The exhaust manifold pressure
estimator is validated using a series of wastegate steps. The exhaust pressure
estimation is designed for steady-state conditions and the validation shows that
it works well and converges within 1 to 4 seconds. Finally a method to detect leakages in the exhaust manifold is suggested.
Leakage detection before the three way catalyst is important since untreated
emissions leak out and since, due to standing waves in the exhaust system, air
can leak in and disturb the air/fuel ratio controller. To extend the operating
region for the detection, the proposed method utilizes both information on leaks
out of the manifold and information on presence of oxygen in the exhaust
manifold.
Per Andersson
2002
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Last updated: 2021-11-10
