Often some car owners say that after driving their car for a while, they find that the engine becomes louder. In fact, as long as the engine is not a problem, then its noise change is not large during its service life cycle, and the owner basically cannot feel it. So why can some cars feel the engine sound become louder after driving for a while? Today we will talk about this topic.
Engine noise is not easy to change
All moving parts of the engine produce a certain vibration to make a sound when working, and the sound emitted by each part is different in size, and finally mixed together to form the engine noise we hear. For example, oil pumps, water pumps, injectors, valves, camshafts, high-pressure oil pumps for direct injection vehicles, timing chains, timing belts and so on. The essence of sound is that the object vibrates, so as long as these parts are not in trouble, then the sound it emits at different vibration frequencies will not change. Just like a person's voice does not change, but when the throat is inflamed, the voice changes.
If the noise of these components changes, there must be a problem with the components themselves, either excessive wear or abnormal movement. For example, the valve clearance was originally 1 mm, and later due to wear and tear, the clearance increased to 2 mm, then the force of the valve rocker arm knocking on the valve will change, and the noise will increase. The piston normally cooperates smoothly with the cylinder and rubs, but when the engine has a problem, we can hear the "banging" sound caused by the piston skirt hitting the cylinder wall when the cylinder is knocked.
Therefore, as long as the engine is not a problem, then its "accent" will not change. So what may be the cause of the sudden increase in the sound of the engine in the daily car? Here are some of the situations I've encountered.
1. Oil viscosity changes
The influence of oil viscosity on engine noise is still relatively large, and the increase or decrease of viscosity may cause changes in engine sound. Because the oil can buffer the impact force between the moving parts, the impact noise between the various moving parts of the engine will become smaller after the oil viscosity is improved, from crisp to dull, that is, the high-frequency sound is reduced and the low-frequency sound is increased. After the oil viscosity is reduced, it changes from dull to crisp, that is, the low-frequency sound decreases and the high-frequency sound increases.
But whether it is bigger or smaller depends mainly on which sound the driver is more sensitive to, some drivers are more sensitive to high-frequency sounds, so after changing the low viscosity oil, the high-frequency sound emitted by the moving parts increases, and he will think that the noise has become louder. However, after changing the high viscosity oil, the high frequency noise was reduced, and he thought the engine was quieter. And some drivers are sensitive to low-frequency sound, so after changing the high viscosity oil, the engine sound becomes dull, he thinks that the noise has increased, and after changing the low-viscosity oil, the high-frequency sound has increased, and he will feel that the engine noise has decreased.
Therefore, whether the engine noise increases or decreases after changing the oil mainly depends on which frequency the owner is more sensitive to the sound of which frequency.
2. Engine knock
Under normal circumstances, the mixture in the engine starts to burn from the electrode of the spark plug, and then the flame spreads outward, so that the pressure in the cylinder rises steadily, the piston is evenly forced, the movement is stable, and the noise is very small. When the deflection occurs, the mixture burns at almost the same time, the pressure in the cylinder increases instantaneously, and the uneven force of the piston will cause rapid vibration, which causes the piston to swing quickly left and right to hit the cylinder wall, at which time it will emit a "banging" knocking sound.
Generally in the summer to open the air conditioner low speed loose clutch moment is the most likely to occur, because the summer temperature is high, the intake temperature is high, and the opening of the air conditioner increases the engine load, the driver in the low speed loose clutch to step on more throttle, the pressure in the cylinder will rise, if the clutch is loose fast, it is easy to knock the cylinder. If the cylinder is frequently knocked, it will cause damage to the cylinder wall, resulting in the phenomenon of pulling the cylinder. So driving in the summer if you frequently hear the engine knocking sound, you can consider raising the number of gasoline, because its explosion resistance is better. It can also be avoided from the operation, such as stepping on the throttle before loosening the clutch, and then slowly loosening the clutch after the engine speed begins to increase.
3, the increase in engine load leads to louder noise
What is engine load? Simply put, it's the depth of the throttle you're stepping on. The deeper the throttle is pressed, the greater the engine load. For example, when you drive a hill, the power is insufficient, under normal circumstances, you should downshift, but you did not downshift, just stepped on the throttle a little more, at this time the engine intake increased, but the resistance has not changed, at this time the combustion of the mixture is more, the combustion speed becomes slower, which will lead to the engine sound muffled.
4. The sound of variable valve timing system starting
I remember a friend who asked me before, saying that his new car had only been bought for less than half a year, and once when he overtook on the expressway, he found that as long as the speed was close to 3,000 rpm, the sound of the engine would suddenly become louder, and he wondered if there was something wrong. Later, after trying the car, it was found that it was not a fault, but the sound of the variable valve timing system.
Because his car has an intake variable valve adjustment, which is what we often call VVT, but his is not a continuous adjustment, only after the engine speed and load reach a certain level. After he bought a car, because it was a new car, he usually drove very carefully and did not slam on the accelerator very much. And that day just because of the need to overtake so the throttle was stepped on, the result of VVT start, adjust the timing of the opening and closing of the intake valve, causing a change in the intake volume of the engine, so that the sound changed.
In fact, this is a very normal phenomenon, indicating that the engine has entered the high-speed operating range, and the VVT system is adjusting the timing of the opening and closing of the intake valve, the purpose is to improve the power of the engine at high speed, so there is no need to worry about this situation, at this time the engine is "opening and hanging".
5. Body resonance noise
This is obvious in some cars where NVH is not doing well, the so-called NVH is the abbreviation of Noise (noise), Vibration (vibration) and Harshness (harsh sound), which mainly refers to the level of vibration and noise suppression in vehicle operation.
Because the car in the operation of the engine, gearbox, brakes, transmission system and many other parts will vibrate, and the body is a good vibration conductor, so when you put a variety of vibration parts are installed on the car after the various vibrations are gathered, it will lead to the driver sitting in the car can feel all kinds of shaking and noise. So manufacturers need to find a way to deal with these vibrations and noise, which is called NVH. But it is not easy to dispose of these things, and it requires a lot of testing and the use of various technical means, which will undoubtedly increase development costs and development time. Therefore, some economic cars are not so well placed in this regard due to cost control, and it is easy to appear at a certain speed or speed to transmit too much vibration or noise to the cockpit, giving the driver the feeling that the car becomes noisier.
For example, a certain model I have driven, 5 gears, the speed is between 1500-2000, as long as the throttle is slightly stepped on the body will have obvious resonance, the steering wheel is shaky, but as long as it passes through this range, it will be quiet immediately.
6, exhaust noise becomes larger
Because the piston movement speed is very fast when the engine is working, so the expansion force generated by the combustion of the mixture can not be fully acted on the piston, such as the work stroke has ended, the piston began to run upwards, at this time the cylinder mixture still has a certain pressure, at this time the exhaust valve is opened, these high-pressure exhaust gases instantly rush out of the exhaust valve, the speed is basically close to the speed of sound, so there will be a lot of exhaust noise, if you have heard some cars without exhaust pipes You will understand, it is as loud as firecrackers. Therefore, the engine must be installed with exhaust pipes, and there is a muffler on the exhaust pipe, which is to reduce the exhaust noise.
If the exhaust pipe leaks or the silencer is damaged, it will cause the exhaust noise to increase, this failure is actually very easy to judge, because the sound originates from the exhaust, which has nothing to do with the engine itself, and the sound of gas expansion is emitted, such as the "popping" sound like a firecracker, which is mostly the front end of the exhaust pipe leaks, because the front end exhaust gas energy is large, and the sound produced is very sharp. It may also be the same "sudden" sound as the tractor, which is mostly a problem with the muffler in the rear section of the exhaust pipe, because the energy of the exhaust gas is greatly reduced here, so the sound frequency is low.
7. The noise caused by the fault becomes larger
The noise caused by the fault is actually very easy to distinguish, because in addition to the noise generated by the knock mentioned above, most of the other noises are naturally increased by the engine sound, just like people talking to raise their voices, you can still hear his voice. The noise caused by the fault is often accompanied by a noticeable abnormal sound, which you have never heard before, and it obviously feels abnormal when you hear it.
The most common is the knocking cylinder, which is caused by the excessive swing amplitude of the piston during reciprocating movement, and the frequency of sound is relatively close to the "click" sound produced when the injector is working, which is a "click" or "click" sound. Generally speaking, knocking cylinders will cause pulling cylinders, because knocking cylinders is a piston that repeatedly hits the cylinder wall, the impact force is too large, and it will soon lead to cylinder wall damage, which is what we often call pulling cylinders.
There is also a timing chain that also produces noise, such as a problem with the chain tensioner, which increases the amplitude of the chain and produces a rattling sound.
Loose timing chain can easily cause engine timing deviation, which will also lead to abnormal engine work and increased noise. When the timing error is wrong, the engine will emit a diesel-like "click" sound, and some people feel like a "rattling" sound, in short, very similar to the crisp and pleasant sound when the diesel car throttles. If there is such a sound, most of them are on time. Timing problems will also lead to intake tempering, that is, the flame in the cylinder will ignite the mixture in the intake manifold, which will make a thumping sound.
In short, if the engine is working normally, then its noise level will not increase, even if hundreds of thousands of kilometers of wear and tear occur, as long as it is in its life cycle, the noise increase caused by it is very small, for the owner can not feel it at all. And the engine really appears to be louder, either it is the normal situation we mentioned earlier, or the engine is really wrong.