Conclusion
Instantaneous speed fluctuations of thermal engines. Excitations applied to the crankshaft

This article shows that the motor's instantaneous excitation torque can be obtained in two different ways, either from the liner-piston force ${\overrightarrow{F}}_{cp}$, or from the connecting rod-crank pin force ${\overrightarrow{F}}_{bm}$. The analytical expressions of these forces are given in two forms, an exact form and a simplified form following power developments of λ.

For a single-cylinder engine, we give the exact formulation of the excitation torque C_m1(F_cp) produced on the crankshaft by the liner-piston force: