Steady state condition refers to the condition under which the vehicle travels at a constant speed in a certain position and a certain engine speed and torque under certain road conditions. Under this condition, the speed and torque of all components of the drive system are fixed values.Strictly speaking, this condition is seldom encountered.
In practical application, it is considered that the operating conditions of rotating speed and torque which vary within a certain range allowed near their own average value are steady-state operating conditions.Under steady-state conditions, the vibration of gear drive system mainly comes from external engine excitation and internal gear engagement excitation.
Engine excitation consists of cylinder gas pressure with periodic change of engine, reciprocating component inertia force and tangential excitation moment with periodic change of gravity.The engine single cylinder torque is:
In the formula, Mp is the excitation moment of gas pressure to crankshaft, Mj is the inertia force excitation moment of reciprocating components, and Mg is the excitation moment of gravity of reciprocating components, respectively, as shown in the formula.
The engine flywheel end output torque is the vector sum of the torques received on each crank
The mean value of the torque and the sum of a series of simple harmonic torques with different amplitudes, frequencies and initial phases can be obtained by means of the Discrete Fourier Transform.
The engine of a heavy-duty vehicle studied is a type cylinder stroke diesel engine. When the engine operates at full throttle rated speed, the average speed, average torque and output power are all equal.Taking the front harmonic torque excited by the engine, the fluctuating torque of the engine at full throttle rated speed is shown in the figure.