Analysis of the Relationship Between Mean Indicated Torque and Its Waveform for Modern Common Rail Diesel and Gasoline Engines

The paper presents the progresses made for the development of a methodology useful for torque estimation, necessary in modern management strategies in order to obtain an indication of the torque produced by the engine. The model developed allows estimating mean indicated torque, cylinder by cylinder, based on instantaneous engine speed fluctuations. The speed signal is picked up directly from the sensor facing the toothed wheel mounted on the engine for control purposes. The engine speed fluctuation amplitudes depend in fact on the combustion and the amount of torque that is being delivered by each cylinder. It is easy to understand therefore how these two quantities, engine speed fluctuation amplitudes and torque production, are strictly connected. The presented methodology is based on two main steps. The first step relies on the identification of the dynamic system model that allows to get torque harmonic from the corresponding engine speed components. The identification could be done by two methods, the first one requiring the knowledge of the value of the reciprocating masses with high precision, and the other one making use of different tests at the same speed but with different loads, in order to estimate separately both the reciprocating masses and the system model. The second step, which constitutes the main focus of this paper, relies on the identification of the relationship between the mean indicated torque and its harmonics. The study of this relationship has been carried out in particular in this paper for a multijet diesel engine and for a gasoline engine. Many tests were performed on different driveline configuration, both in a test-cell, and on-board. Once indicated torque and its harmonic components have been evaluated from in-cylinder pressure signals, identification of the relationship has been possible. Influence of the type of combustion performed has been discussed, as also the effects related to cylinder filling and injection timings.