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Six Degrees Crankshaft Individual Air Fuel Ratio Estimation of Diesel Engines for Cylinder Balancing Purpose

2006; Linguagem: Inglês

10.4271/2006-01-0013

2688-3627

J. Chauvin, Nicolas Petit, Pierre Rouchon, Philippe Moulin, Gilles Corde,

Vehicle emissions and performance

In the context of modern engine control, one important variable is the individual Air Fuel Ratio (AFR) which is a good representation of the produced torque. It results from various inputs such as injected quantities, boost pressure, and the exhaust gas recirculation (EGR) rate. Further, for forthcoming HCCI engines and regeneration filters (Particulate filters, DeNOx), even slight AFR un- balance between the cylinders can have dramatic conse- quences and induce important noise, possible stall and higher emissions. Classically, in Spark Ignition engine, overall AFR is directly controlled with the injection system. In this approach, all cylinders share the same closed- loop input signal based on the single ¸-sensor (normal- ized Fuel-Air Ratio measurement, it can be rewritten with the total and air masses in the exhaust manifold as ¸ , 1 i M air MT ). Ideally, all the cylinders would have the same AFR as they have the same injection set-point. Unfortu- nately, due to inherent flaws of the injection system (pres- sure waves, mechanical tolerances, ...), the total mass of fuel injected in each cylinder is very difficult to predict wi th a relative precision better than 7%. Having a sensor in each cylinder would enable an accurate individual con- trol. In practice, cost and reliability of multiple ¸-sensors prevent them from reaching commercial products lines. In this context, individual cylinder AFR estimation can give crucial information to get the HCCI running better. The contribution of this paper is the design and experi- mental tests of a real-time observer for the individual cylin- der AFR using the reliable and available ¸-sensor placed downstream the turbine as only measurement. In pre- vious works, the methods used to reconstruct the AFR of each cylinder from the UEGO (Universal Exhaust Gas Oxygen) ¸-sensor measurement are based on the permu- tation dynamics at the TDC (Top-Dead Center) time-scale and a gain identification technique. Here, we propose a higher frequency approach (6 degree crankshaft angle modelling and update instead of 180(TDC)). We design an observer on the balance model of the exhaust and de- sign a high frequency observer to solve the problem. We use a physics-based model underlying the role of periodic input flows (gas flows from the cylinders into the exhaust manifold). The observer is validated experimentally on a 4 cylinder HCCI engine. As a conclusion, we provide re- sults of closed-loop control using the proposed technique to prove the relevance of this approach.