Cylinder Charge Estimation in Diesel Engines with Dual Independent Variable Valve Timing

Abstract

Abstract With stricter emission legislations and demands on low fuel consumption, new engine technologies are continuously investigated. At the same time the accuracy in the over all engine control and diagnosis and hence also the required estimation accuracy is tightened. Central for the internal combustion control is the trapped cylinder charge and composition. Traditionally cylinder charge is estimated using cycle averaged manifold pressures and engine speed in e.g. two dimensional look-up tables. With the introduction of variable valve timing, two additional degrees of freedom are introduced. To incorporate support for these new dimensions in a traditional look-up table estimation approach would be rather expensive in terms of model calibration and collection of empirical data. This is especially true if the cam phasers are given large enough authority to offer the powerful thermal management capabilities required to fulfill future emission legislations. Two semi-physical models for pumped mass flow through the engine are developed and evaluated on experimental data. Both utilize crank angle resolved manifold pressures and cylinder volumes at discrete valve events, e.g. intake valve closing. The data covers a large operating region in engine speed/load and large independent variations in both intake and exhaust valve timing, including valve overlap and symmetric/asymmetric underlap.