Optimization of HEV Vehicle’s Engine Modulated Noise

One 1.5L Miller-cycle turbocharged four cylinder gasoline hybrid engine is installed on a certain hybrid vehicle. When accelerating at low to medium speeds with a small throttle, there is a "da da" knocking noise inside the car, which seriously affects the overall sound quality of the vehicle. By analyzing the vibration and noise data of the engine, it was found that the frequency of the abnormal knocking sound is 200-1000Hz, which presents a half order characteristic in the time domain, that is, one knocking occurs when the engine crankshaft rotates twice. Through Hilbert demodulation analysis of the vibration data in the problem frequency range, it was found that the knocking noise was modulated in the frequency domain, with a modulation frequency of half of the crankshaft rotation frequency. By building a fully flexible multi-body dynamic model of a hybrid powertrain and inputting the engine's cylinder pressure excitation, the combustion excitation is coupled with mechanical vibration noise to simulate the surface vibration of the powertrain. Measures such as optimizing the cylinder pressure curve by adjusting spark angle and scavenging angle,and improving crankshaft stiffness by increasing the overlap between mainbearing diameter and connecting rod diameter, the sound quality issue of this hybrid model has been significantly improved under low speed and low throttle acceleration conditions.