Electronic Throttle Control systems substitute the driver in commanding throttle position, with the driver acting on a potentiometer connected to the accelerator pedal. Such strategies allow precise control of air-fuel ratio and of other parameters, e.g. engine efficiency or vehicle driveability, but require detailed information about the engine operating conditions, in order to be implemented inside the Electronic Control Unit (ECU). In order to determine throttle position, an interpretation of the driver desire (revealed by the accelerator pedal position) is performed by the ECU. In our approach, such interpretation is carried out in terms of a torque request that can be appropriately addressed knowing the actual engine-vehicle operating conditions, which depend on the acting torques. Estimates of the torque due to in-cylinder pressure (indicated torque), as well as the torque required by the vehicle (load torque), must then be available to the control module. The estimation procedure should be at the same time sufficiently precise and fast in order to comply with the driver requests in real time. In this paper we present a signal processing procedure to estimate the cycle mean values of both the indicated and load torque, based on a frequency analysis of the engine block vibrations signal. The algorithm that has been developed tries to meet the precision and quickness requirements for on board implementation; this goal has been reached using only two frequency components of the engine block vibrations. The quality of the estimation methodology has been initially tested on an engine test cell, using a two cylinder small diesel engine and showing a good agreement between measurements and estimations, even under strong speed and load transients. The procedure is scheduled to be validated on-board a production vehicle.
Air-Fuel Ratio Control for a High Performance Engine using Throttle Angle Information
Author: Piero Azzoni, Giorgio Minelli, Davide Moro, Massimo Ceccarani, Giorgio Rizzoni
This paper presents the development of a model-based air/fuel ratio controller for a high performance engine that uses, in addition to other usual signals, the throttle angle to enable predictive air mass flow rate estimation.
The objective of the paper is to evaluate the possibility to achieve a finer air/fuel ratio control during transients that involve sudden variations in the physical conditions inside the intake manifold, due, for example, to fast throttle opening or closing actions. The air mass flow rate toward the engine cylinders undertakes strong variation in such transients, and its correct estimation becomes critical mainly because of the time lag between its evaluation and the instant when the air actually enters the cylinders.
The approach to research consists of the use of a fuel film dynamics model-based compensator and of an algorithm that estimates, before the intake stroke, the amount of air that will enter the cylinder, using the throttle position signal as a feed-forward information about the mean intake manifold pressure.
The conclusion will show the possibility to enable some improvement in the air-fuel ratio control; experimental tests on-board the vehicle are in progress.