Discussion on: Adaptive Estimation of the Engine Friction Torque

The paper by A. Stotsky introduces an algorithm for real-time estimation of the engine friction torque, capable to achieve a dynamic adaptation of the static maps widely used in the engine control functionality. This adaptation of the friction map allows a better vehicle driveability performance and an enhanced control by the driver of the vehicle longitudinal transients. There are several interesting features of the approach proposed by the Author, while the discussion will focus on four issues that may be seen as suggestions for further development: (i) analysis of cold start condition, (ii) accessories torque; (iii) working condition other than idling; (iv) effects of engine wear. As first, since the method aims to improve the vehicle comfort and driver’s control, the possibility to get friction torque assessment during cold start with consequent map and look-up table adaption is given by the theoretical models and experimental outcomes in [1,2]. The conclusions of these papers underline that, for some tribological pairs, the friction mean effective pressure (fmep1⁄4 4 Tf,avr/V; V is the engine displacement) during cold transient is up to three or four times higher than fmep at warmed up condition. The piston assembly and the crankshaft main bearings contribute significantly to the total engine fmep and the changes in the oil viscosity produced by changes in film temperature are the most substantial influence on friction during cold start and cold running at constant speed. The use of theoretical models for fmep evolution as function of engine average temperature may improve the controller performance during cold start phases. The ECU friction map could be updated by acquiring some points (e.g., 2 4 points as proposed by the Author) during the cold start. The second point deals with accuracy of the instantaneous accessories torque estimate, since some devices can account for up to 40% of the whole Tloss þ Tacs torque, in some conditions [3]. Therefore, the uncertainty on the Tacs has momentous influence on Tloss (and its Tf share calculation); this effect is clearly shown taking into account the relationship for the friction torque deviation evaluation (see Eq (4)):