Analysis and elimination of abnormal noise in automotive engine connecting rod bearings

Analysis and elimination of abnormal noise in automotive engine connecting rod bearings

1、 Phenomenon

When the engine is working, the connecting rod bearing and the shaft neck undergo relative motion and collide, producing a "clunk, clunk" sound, which is called connecting rod bearing noise. The phenomenon is:

When the engine is working, it makes a rhythmic sound of "ga, ga".

The size of the sound varies with the engine speed, that is, the sound is louder when the speed is high; On the contrary, the noise is small.

3. The sound increases with the increase of engine load; On the contrary, the sound decreases.

4. When suddenly accelerating, there is a noticeable continuous' ga, ga 'sound.

2、 Cause analysis

1. The impact of wear and tear

(1) Natural wear and tear

When the engine is working, the gas pressure inside the cylinder always acts on the top of the piston. Due to the action of gas pressure, the piston and piston pin, piston pin and copper sleeve are compressed tightly, and the connecting rod bearing and connecting rod journal, main bearing and main journal are compressed against each other through the connecting rod, resulting in wear during operation and increasing the fit clearance; Due to the action of inertia force, the connection and contact parts of various transmission components are subjected to increased force, which will increase the wear and damage of the components; The centrifugal force generated when the crankshaft rotates acts on the connecting rod journal, causing an additional load between the connecting rod bearing and the connecting rod journal, as well as between the crankshaft main bearing and the main journal, thereby increasing the wear and damage of the components. When the clearance between the bearing and the journal is appropriate and there is lubricating oil as the medium, no noise will be made; If the clearance between the bearing and the journal is too large, it will make a noise.