Method of determining rubbing friction torque in amotor vehicle powertrain

Abstract

A method of determining the rubbing friction torque involves characterizing fuel cutoff engine deceleration, and calculating the rubbing friction torque for any combination of engine speed and powertrain temperature is calculated in accordance with a base point rubbing friction torque RFTbase determined at a base powertrain temperature Tbase and fuel cutoff characterization data. The calibration data characterizing fuel cutoff engine deceleration is obtained by alternately enabling and cutting off engine fuel delivery to cycle the engine speed between specified set points, and measuring and recording the engine deceleration during intervals of fuel cutoff. The rubbing friction torque RFTtest at a given test temperature Ttest is calculated according to RFTtest=(RFTbase+PFTbase)×DECELtestDECELbase-PFTtest,where DECELtest and DECELbase are the fuel cutoff engine decelerations at the test and base points, respectively, and PFTtest and PFTbase are the pumping friction torques at the test and base points, respectively.

Description

TECHNICAL FIELD This invention relates to rubbing friction torque in a motor vehicle powertrain including an internal combustion engine, and more particularly to a method of determining the rubbing friction torque. BACKGROUND OF THE INVENTION The amount of torque an internal combustion engine must produce to compensate the rubbing friction of the powertrain is customarily referred to as the rubbing friction torque. In usual practice, the rubbing friction torque is measured for various operating conditions during engine calibration, and stored in a calibration table as a function of engine speed and powertrain temperature. During subsequent engine operation, the engine controller accesses the rubbing torque calibration table as part of its computation of engine output torque for various control algorithms such as electronic throttle control and electronic transmission control. Measuring the rubbing friction torque is ordinarily accomplished by using an engine dynamometer to motor ...

AI Technical Summary

Benefits of technology

The present invention is a method for calculating the rubbing friction torque of a fully assembled motor vehicle powertrain at different engine speeds and temperatures. This is done by using a base rubbing friction torque determined at a base point powertrain temperature and calibration data characterizing fuel cutoff engine deceleration as a function of engine speed and powertrain temperature. The calibration data is obtained by alternately enabling and cutting off engine fuel delivery to cycle the engine speed between specified set points, and measuring and recording the engine deceleration during intervals of fuel cutoff. The rubbing friction torque at a given test point is calculated from the base rubbing friction torque using a formula based on the engine deceleration at the test and base points. This method allows for more accurate calculations of rubbing friction torque and can help improve the performance and efficiency of motor vehicles.

Problems solved by technology

Obviously, this can be a costly and time-consuming process, and can be performed for only a limited range of engine temperatures.

But the moment of inertia I is difficult to estimate, and any estimation error is magnified by the engine acceleration which may be quite large.

Although it is theoretically possible to obtain the test data at zero acceleration so that the term I(dω / dt) is zero, such test conditions are difficult to achieve as a practical matter.

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