Estimation of Indicated– and Load– Torque from Engine Speed Variations

The importance of control systems and diagnostics in vehicles are increasing and has resulted in several newmethods to calculate better control signals. The performance can be increased by calculating these signals close to optimum, but that also require more and precise information regarding the system. One of the wanted control signals are the crankshaft torque and the thesis presents two different methods to estimate this torque using engine speed variations. These methods are Modeling of the Crankshaft and Frequency Analysis. Themethods are evaluated and implemented on for a four cylinder SAAB engine. Measurements are made in an engine test cell as well as a vehicle. The results show that the Modeling of the Crankshaft method does not produce a satisfying estimation, with a difference of about 200% between estimated and calculated torque. On the other hand, the Frequency Analysis provides an accurate estimation of both mean and instantaneous indicated torque, with a maximum difference of ±20% between estimated and calculated torque.