Common faults of exhaust muffler

The principle of a car silencer is that its exhaust pipe is composed of two pipes of different lengths, which are separated before they meet. Because the difference between the lengths of the two pipes is equal to half of the wavelength of the sound waves emitted by the car, the two columns of sound waves cancel each other and interfere with each other to reduce the sound intensity when superimposed during superposition, so that the sound is reduced, so as to achieve the effect of sound attenuation.

This article contains the following:

• Common faults of exhaust muffler

• Fault phenomenon

• Failure analysis

1.Common faults of exhaust muffler

Automobile muffler is a special equipment that prevents sound transmission and allows airflow to pass through, and prevents dynamic noise of airflow. At present, in order to suppress the environmental noise caused by the discharge of high-pressure airflow, there are many types of mufflers in the world, and most of them adopt the principle of impedance compound muffler. Due to the complex structure, heavy weight, high-temperature oxidation sound-absorbing filler, high-speed airflow impact sound-absorbing filler, and water vapor penetration sound-absorbing filler, etc., the muffler is frequently repaired, the noise reduction effect is poor, and the service life is short. The main problem facing the device.

2.Fault phenomenon

A Dongfeng EQ1090D car has a blasting phenomenon in the muffler during driving. During the parking inspection, when the ignition coil high voltage main line is unplugged, test fire at 34mm from the cylinder, pull the distributor power-off contact or shake When turning the crankshaft, the flashover was normal, but it was found that the distributor's power-off contact was ablated. After grinding the contacts with sand bars and adjusting the gap to 0.35-0.45mm, the engine runs normally after starting, but when the car travels about 40 kilometers, the muffler has shot again.

Fault inspection and elimination: According to the above phenomenon, the cause of the muffler firing was carefully analyzed. To find the crux of the fault, the ignition sequence, the spring force of the power arm of the distributor, the ignition timing, and the spark plug were not found. Continue to check the carburetor air filter, valve clearance and no results. Starting the engine again and running normally, but it didn't take long for the old disease to recur.

Stop and check the distributor section again. Through disassembly and careful inspection, it was finally found that the copper wire from the contact arm of the disconnector to the low-voltage terminal was broken at the bend, leaving only a few thin copper wires connected. After replacing the broken copper wire, the fault disappeared.

3.Failure analysis

When the copper wire of the low-voltage wire part of the distributor is broken, the cross-sectional area of the wire decreases, thereby increasing the resistance of the primary circuit and reducing the current in the circuit, resulting in insufficient high voltage generated by the ignition coil. When the engine temperature is low, although it is more difficult to start, the engine can run normally after starting. After the temperature of the engine rises, the temperature of the ignition coil rises, and the resistance increases as the temperature rises, so the high-voltage electricity generated by the ignition coil will be more insufficient, the high-voltage sparks will be weaker, or even cut off. Due to the misfire from time to time, the unburned combustible gas mixture in the cylinder is discharged into the muffler. When it expands in the muffler, it will deflagrate when it encounters the sparks in the exhaust gas, which is shown as the muffler firing.

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