After the car starts, the engine has a belt creaking sound, and after running for a while, it is gone, what is the problem?
On the surface, it is a problem of the belt, but in essence it is a problem of the automobile power generation system.
When the car starts, it needs to consume a lot of electrical energy, which is supplied by the battery. When the engine is working normally, the generator needs to replenish the consumed power to the battery. Therefore, the generator is working at full capacity for a period of time after the engine is started. If the battery is also used during engine downtime and consumes more power, then the generator will work at full capacity for a longer period of time.
The generator is driven by the engine crankshaft through the belt, and the ratio of the two is about 1:2.5. That is, the engine crankshaft turns once and the generator turns two and a half turns. The purpose of this is to keep the engine at a low speed and the generator to generate electricity normally (the engine also generates electricity when idling). The generator works by cutting the wires of magnetic field to generate current. After the generator rotor coil is energized, a magnetic field is generated, and when it rotates at high speed driven by the engine, the stator coil continuously cuts the magnetic field line of the rotor coil, which generates an electric current. The external output of these currents through a certain rectification is the working process of the generator.
In this process, the wire cutting magnetic field wire will produce resistance, the faster the cutting speed, the greater the power generation, the greater the resistance. The power of the generator is generally between 0.8 and 1.5kw, and when working at full load, it will consume 1.5kw of engine power (so the car's electricity will also increase fuel consumption). Some small-displacement engines will shake after turning on the headlights, and the car will not be able to accelerate, because the generator consumes part of the power). This power is transmitted to the generator through the belt, if the belt can not withstand such a large load, it will slip on the pulley, rubbing against the pulley to make a squeaking sound.
Generator belts are generally multi-slot wedge belts. When the engine is designed, the power and torque that the belt can transmit are precisely calculated, which will certainly exceed the maximum power of the generator. However, after the belt is used for a long time, the wedge groove of the belt will wear out and the surface friction coefficient will decrease; at the same time, the crankshaft pulley and the generator pulley will also wear, the groove depth will increase, and the surface friction coefficient will decrease. In this way, the power and torque that the belt can transmit are reduced, and when the generator is working under heavy load, the belt cannot withstand the power and torque transmitted by the engine crankshaft, and it will slip on the pulley and make a squeaking sound. The higher the engine speed, the louder the noise.
When the generator is fully loaded for a period of time, the power of the battery is almost replenished, the generator will reduce the power generation power, and the power and torque transmitted by the belt will be reduced. When the power generation power is lower than the power that the belt can withstand, the belt can transmit all the power, it will no longer slip, and the squeaking sound will disappear.
So what's wrong with this noise? Will the engine be damaged? If it is only a little bit of a cold start, and then it disappears, this situation is no problem, the belt has a certain aging, the pulley has a certain wear, has not yet reached the level of replacement, or the cost of replacement is too large, there is no need. If it has been ringing, it means that the belt aging is too serious and needs to be replaced; it may also be that the belt tensioner is loose or damaged, the belt tension is reduced, and the friction between the belt and the pulley is reduced, resulting in the slip of the two, at this time, just readjust the tensioner. The generator belt slips without any damage to the engine, which can be assured.
There is no clear replacement cycle for the generator belt, and it can generally be used for six years and more than 100,000 kilometers. If you find small cracks, broken strands, etc. on the generator belt, you need to replace it. If the generator belt breaks during driving, the generator stops generating electricity, and the car will soon break down, which is also more dangerous.