Mechanical sources of permanent excitation
Torsional rotor dynamics - Types of permanent excitation

The connecting rod exerts a cyclic force on the crankshaft crankpin, the tangential component of which gives a torque C that can be broken down into a C_p component due to the action of the pressure on the piston and a C_i component due to the quantities of acceleration of the connecting rod and piston. We have :C = C_p + C_i

For a constant crankshaft speed Ω expressed in radians per second, we can calculate the periods τ of the two components of the total torque. We obtain :