When the diesel engine is in normal working condition, the sound it gives out is a steady, rhythmic and coordinated sound. If the engine in the process of operation, accompanied by other sounds, such as intermittent or continuous metal percussion sound, continuous metal friction sound, that indicates that the engine is not running normally, this sound is called abnormal sound of diesel engine. The abnormal noise of diesel engine is an important form of engine fault and an important basis for judging and analyzing faults. Once abnormal sound appears, it indicates that the technical condition of a diesel engine has changed. The abnormal noise of diesel engine has certain regularity. If we can master the abnormal noise characteristics of diesel engine, it will be of great help to diagnose and eliminate diesel engine faults.
1．Sound closely related to the engine speed
Diesel engine most common abnormal sound, depends on the diesel engine speed state. When the speed of the diesel engine changes, the motion speed of the moving parts will also change, especially in the case of rapid acceleration or deceleration, the moving parts will produce certain acceleration or deceleration. Due to the effect of inertia, on the one hand, it may cause new abnormal sound, on the other hand, it will make the difference that is not obvious become clear. Therefore, the existence of most common abnormal noise faults of diesel engine largely depends on the rotational speed state of diesel engine.
Based on the analysis of judgment diesel engine failure in the different day, should do more various speed test, in order to accurately locate sound the cause of the problem.
(1)Suddenly step on the gas, diesel engine speed increases, the more obvious and clear sound, such as main bearing and connecting rod bearing kuang sound, the sound of piston ring friction.
(2)Diesel engine speed stability, sound disorder, sharp slowdown, performance is relatively clear sound, such as piston pin bushing loose kuang, CAM shaft axial clearance is too large to produce noise, etc.
(3)Diesel engine idle speed or low speed, the more clear sound, such as a piston pin or connecting rod bearing assembly of tight ring, piston pin, valve and valve lifter have abnormal sound, etc.
(4)Sound of medium speed diesel engine, such as valve seat ring is loose to produce sound, camshaft sound from the outside profile of wear, etc.
2．Sound closely related to the diesel engine load
The stress state of each moving part of diesel engine changes with the change of load, and the abnormal sound will also change accordingly. Some abnormal noise is reduced with the decrease of load. Some abnormal noises are aggravated with the decrease of load. Some abnormal noises are generated with the change of load. The abnormal noise caused by the load is obviously related to the cylinder position of the diesel engine.
When analyzing and judging the abnormal sound fault of diesel engine, the relationship between abnormal sound and the load can be judged by suddenly increasing the load, decreasing the speed, or suddenly reducing the load and increasing the speed. The multi-cylinder diesel engine can be judged by the method of disconnecting the fire of each cylinder or two adjacent cylinders to relieve the load of one or two cylinders.
(1)Single cylinder diesel engine load increase, abnormal sound increase generally piston cylinder, connecting rod bearing sound; With the decrease of load, the abnormal sound usually includes the ring ring of valve seat and the sound produced by individual parts of valve mechanism.
(2)For multi-cylinder diesel engines, if a cylinder fire, abnormal sound to reduce or disappear, it is generally piston knock cylinder, piston ring air leakage or connecting rod bearing loose sound; If a cylinder is broken off, abnormal sound is aggravated, or there is no sound before, but sound appears instead, it is generally the sound caused by loose loose piston pin sleeve and loose connecting rod bearing cover or flywheel fixing bolt; If two adjacent cylinders break fire, the abnormal sound is reduced or disappeared, then the main bearing loose sound.
3．Sound with the diesel engine work cycle occur regularly
The crank-connecting rod mechanism and some parts of the valve mechanism of the four-stroke diesel engine, or the working cycle between the parts and the diesel engine have regular movement and contact, so some abnormal sound rules are also fixed. Therefore, when analyzing the abnormal sound fault, we should first diagnose the abnormal sound with regularity.
(1)If the piston cylinder sound, then, every turn of the crankshaft, it will sound once; And in each cycle, the combustion expands to do work once, and the crankshaft turns twice, and it rings twice. Therefore, the crank linkage mechanism in a movement caused by the sound, are issued twice for each cycle. Such as piston pin knock, connecting rod bearings loose and air leakage ring sound.
(2)If the valve sounds, the camshaft turns once for every two turns of the crankshaft. So the valve only rings once; That is, each cycle, the combustion expansion does work once. The valve rings once. In turn, the sound caused by a moving part in the valve mechanism is emitted once per cycle. Such as valve spring fracture, tappet and its guide hole clearance is too large, CAM profile wear, valve ring loose and camshaft timing gear radial rupture caused by sound.
4．The sound of diesel engine temperature sensitive
(1)Low temperature sound, temperature rise after the sound attenuation, or even disappear. The cause of the noise is: piston and cylinder wall clearance is too large; The piston is out of alignment due to the depth and width of the oil groove of the main bearing; Low oil pressure and poor lubrication.
(2)When the temperature rises, the sound will decrease or disappear. The causes of the noise include: premature combustion caused by overheating; The long and short axes of the piston skirt ellipse are opposite. The piston ellipticity is small and the clearance between piston and cylinder wall is too small. Piston deformation; Piston ring clearance is too small.
5．Sound often accompanied by other diesel engine fault phenomena
The abnormal sound of diesel engine often leads to other faults. If the oil pressure drops, poor lubrication; Unsteady rotation speed and fuselage shake; Poor startup and insufficient power; Increased fuel consumption, abnormal smoke, etc. These fault phenomena are helpful for accurate analysis, judgment and elimination of abnormal noise fault. For example, the connecting rod bearing is too loose, the intake and exhaust door is stuck, the piston and the cylinder wall clearance is too large, not only can produce sound, but also can lead to oil pressure drop, individual cylinder does not work, add oil mouth pulsation smoke and other fault phenomenon.