Analysis of engine noise of small excavator

After analyzing the small excavator, it was found that its main noise sources include: engine noise, hydraulic system noise, mechanical transmission noise for getting on and off the vehicle, and body resonance noise (due to the thin body covering sheet metal parts, the excavator covers parts when constructing or walking) prone to resonance), and resonance noise in the cab (due to the narrow space in the cab, the noise cannot be effectively absorbed and resonate with each other due to collision), etc. Among them, engine noise contributes the most and is a key factor to be considered in noise reduction planning.

1. Analysis of the sources of noise from small excavator engines

1. Engine exhaust noise

The exhaust noise of small excavators is the main part of the engine's aerodynamic noise. Its noise is generally 10~15dB(A) higher than the overall engine noise. It is the first part that needs to be controlled for noise reduction. Engine exhaust noise mainly consists of the following components:

(1) Low-frequency pulsating noise caused by periodic exhaust gas;

(2) Air column resonance noise in the exhaust pipe;

(3) Helmholtz resonance noise of the cylinder;

(4) Injection noise occurs when high-speed airflow passes through the exhaust valve annular gap and curved pipes;

(5) Eddy current noise and regenerative noise generated by the exhaust system under the stimulation of pressure waves in the pipe. Eddy current noise has a continuous high-frequency noise spectrum, with frequencies above 1000Hz. As the air flow speed increases, the frequency will increase significantly.

2. Engine mechanical noise and combustion noise

The mechanical noise of small excavator engines is mainly caused by the oscillation or mutual impact of the moving parts in the engine caused by the periodic effects of gas pressure and moving inertia force during operation; combustion noise refers to the structural oscillations generated during the combustion process and noise. The sound pressure level of combustion noise (especially the low-frequency part) in the engine cylinder is very high. However, most parts in the engine structure have high rigidity, and their natural frequencies are mostly in the mid-to-high frequency range, because they do not respond to the frequency of sound wave propagation. Therefore, the very high cylinder pressure level peak in the low frequency band cannot be transmitted smoothly, while the cylinder pressure level in the medium and high frequency bands is relatively easy to transmit.