Chassis performance is also metaphysics?

NVH-noise, vibration and roughness, "noise, vibration and acoustic vibration roughness".

Vd-vehicle? Dynamics, "vehicle dynamics", can also be interpreted as "chassis performance".

There was a discussion in Zhihu, "Why do many automobile engineers say NVH is metaphysics?" Since then, "NVH is metaphysics" has become a "stalk" and has been mentioned by jokes from time to time in the automotive engineering circle.

You can go and see the discussion on this matter in Zhihu for yourself.

As a chassis performance engineer, I played such a joke with my NVH colleagues and was told: "I don't think NVH is too metaphysical. If you have to talk about metaphysics, I think you chassis people are more like metaphysics. "

At first glance, this is just a joke; On second thought, it still makes sense.

If NVH = no? Very? If you are happy, maybe VD = very? Dramatic (very dramatic).

I also tell a few anecdotes:

1. The chassis adjustment of a certain vehicle was completed. After the test drive, the shock absorber scheme A was not satisfied and the acceptance failed. After a week of continuous adjustment, a new shock absorber scheme B was put forward and compared with the scheme A used in the first acceptance. When the old and new schemes were tested, I forgot to tell the leader that one of them was the old scheme that failed the last acceptance. After the test drive, the leader stated: both schemes are improved from the last acceptance scheme, and the work is worthy of recognition. Comprehensive comparison shows that Scheme A is more balanced than Scheme B, and then Scheme A is decided as the final freezing scheme, and the work is successfully completed.

2. During the steering calibration of a certain model, the leader felt that the steering wheel was light after the test drive, so he adjusted it again. Test drive again, I think it's off again. The engineer was at a loss and happened to be delayed by other urgent matters. The car has been parked there all day. After a day, the leader drove to test drive alone. After returning, he asked the engineer: "What adjustments have been made to the current scheme in the car? It feels good. "

3. Engineer A fixed the driving evaluation route when adjusting the chassis of a certain model. When parking at traffic lights, the steering wheel will automatically deflect to the right, and the deflection is not small. Check the tire pressure, four-wheel alignment and brakes. If another engineer B drives on the same route, the problem will disappear. Finally, I found the reason: on the test drive route, many sections with traffic lights often have large trucks passing by. Over the years, countless large trucks braked suddenly at traffic lights, causing the asphalt pavement on which the wheels of trucks rolled to be depressed, and the pavement section was W-shaped:

In order to prevent the truck from stopping in the blind area of rear view, engineer A once parked his car on the left, even when the traffic lights came first, which was equivalent to stopping on a slope inclined to the right. Engineer b didn't have this habit, and the problem disappeared.

4. The engineer drives his own private car, which makes him feel more shaky, better isolated, and the steering is a bit fuzzy. He suspected that the tire pressure was insufficient. He went to the street tire store to check the tire pressure, and each of the four tires was about 0.2bar lower than the standard. Anyone who tells him will be laughed at and boasted.

5. In the winter morning in the north, the evaluation route of about 20km takes about 40 minutes. Without changing any parts, the car drove twice in a row, and the performance of the second lap was better than that of the first lap.

6. During the chassis adjustment of a certain model, the foreign experts of the shock absorber supplier were very satisfied with the scheme at that time after the test drive, indicating that the balance was good. Results When disassembling the car, it was found that the configuration schemes of the two rear shock absorbers were different.

In the eyes of outsiders, there are too many "mysterious" things about chassis performance, and chassis adjustment is "mysterious". The main engine factory spends tens of thousands of dollars every day, goes out for a ride, comes back with a new plan, goes out for a month, and comes out with the result that "the mountain is the peak". Why?

However, most of the so-called "metaphysics" is ridiculous, and serious engineers don't really regard the engineering science on which they live as metaphysics. All "illusions" come from ignorance, just as most of us look at quantum mechanics. Why do two particles that are far apart "entangle"? How can Schrodinger's cat be both alive and dead? Isn't this metaphysics?

So, fantasy is because we haven't seen the truth and essence yet. Before we knew the truth, two large and small shot put dropped by Galileo from the Leaning Tower of Pisa fell to the ground at the same time, which was simply witchcraft.

In the field of automobile engineering, there are still many things that have not established a scientific mathematical model and are still crossing the river by feeling the stones. Take NVH as an example. Regardless of how unexpected the corresponding reasons are. Let's talk about observing the phenomenon itself. There are many sensors used for NVH testing. Most of how much a car has improved after NVH rectification can be proved by data. Whether the vibration has decreased or not, and the sound pressure level has decreased by several dB, all of which can be said by data. The hard part is that the data can't be measured, such as quality.

The same sound pressure level, some sounds make people feel comfortable, and some sounds make people feel annoying. It is difficult to describe and compare the sound quality completely by data. In addition, different people have different feelings about the same sound. For example, when Jaguar's electric car I-Pace is stepping on the accelerator deeply, the speaker at the door will make the sound of the engine, which sounds like the roar of pressing the ear to me. When it comes to sound, different people have different understandings of good sound.

Well, people in different countries have different understandings of what kind of sports car sounds better. It is true that selling cars in which country should better cater to the general cognition of which country. But who can use the data to describe to me what this "sports" sound is like? What is this "aggressive" voice?

What can't be described by objective data has to be judged subjectively.

Why does a painting become a world classic?

Why a girl can be the champion of a beauty contest;

How a dish wins the hearts of the judges;

All these depend on subjective evaluation, because there is no test method and theory to express why a food is popular in a mathematical way. Even before Leonardo da Vinci painted Vitruzzi, you didn't know why long legs were more beautiful.

Because objective measurement is unattainable, it relies on subjective evaluation; Because of the subjectivity of subjective evaluation, it looks very metaphysical.

Your wife tells you that this color lipstick is more "smart and lively" than the other one, and your heart is like this:

Your friend tells you that this piano piece sounds like Sunshine, and your heart is like this:

Your buddy told you that he has been playing HiFi stereo for a long time, and even the power supply will affect the sound quality. The thermal power is too large, the hydropower noise floor is too cold, and the wind power level is very poor. Nuclear power is suitable for listening to loud voices ... after listening, your heart may be like this:

Because of subjectivity, different people may have different feelings; It is also because of subjectivity that it is difficult to communicate between these different feelings, which is "mysterious".

The witch doctor said that she heard providence when she jumped into the divine world. You can't say it just because you didn't hear it. God must be silent.

Chassis adjustment experts say that the overall feeling of the front suspension is stronger after the modification of XX, and it cannot be said that the performance of the car has not changed without feeling.

What's more, people around say that it has improved. What do you do? Either admit your "stupidity" and feel nothing; Either echo or praise, then in your opinion, this is clearly The Emperor's New Clothes. When you choose the latter, engineering problems go to superstition, and science goes to metaphysics.

However, this matter should be scientific after all, and fantasy is due to ignorance. Of course, the "ignorance" here does not contain any derogatory meaning. Even experts who have worked for decades will inevitably encounter problems of ignorance and mystery.

Why science and not metaphysics?

1, science is clear, metaphysics is not clear. Behind science is a complete theoretical system. All phenomena are supported by facts and theories, which can be justified in principle, and can be confirmed by simpler cases.

It's like saying that you cooked the same food at night as at noon, and put more salt in it at night, but your wife didn't taste the difference, so you can explain:

Because the amount of vegetables and water has not changed, but the amount of salt has increased, which makes the concentration of sodium ions higher and stimulates the bioelectricity generated by taste buds stronger. Nerves send electrical signals to the brain, and the brain will feel more salty; Although you don't feel it now, if I continue to add salt, do you feel salty?

There is also theoretical support and factual basis. Is it scientific? Your wife will definitely say, "I think what you said is very reasonable, but I really want to hit you."

Metaphysics, on the other hand, is not the case. When people tell you that "my uncle died in the first month", they can't tell you why, only tell you that "the secret can't be revealed".

2. Professional science has professional communication terms. When you say that "this piece of music smells of sunshine", different people will have different understandings, and those who don't understand it will think that you are talking about metaphysics. Engineering has norms to follow, and every sentence and every noun has an exact meaning. When others communicate, they say "soft to the touch, completely isolated, and not controlled enough", while you say "this car is' fleshy' when driving"; Others say "linear response, good coordination", while you say "turning like water" Which sounds more mysterious?

The human body is a scientific observation device.

The human body is covered with a considerable number of sensors, large and small, and people can perceive massive information such as temperature, size, hardness and salinity. Although the accuracy of these sensors is indeed limited, it does not mean that the information observed by human body is incorrect or even nonexistent because there is no instrument verification.

Moreover, scientific skill training can upgrade the observation equipment of human body, and more subtle phenomena can be observed more accurately. When someone insists that car A is more comfortable than car B, but you just can't feel the difference, this sentence will sound a little mysterious and you will be suspicious. However, if the emperor's new clothes really exist, then the people you see will not only tell you that the emperor is wearing beautiful new clothes, but also tell you what kind of tattoos are on the clothes, what silk thread is used and what color it appears in the sun. Similarly, a scientific evaluator will not only tell you that the comfort of the car has improved, but also tell you what changes have taken place in the speed-on what road-in what part of the body-in what frequency range.

Finally, mistakes are common. Even precise measuring instruments will have measurement errors, and any observation method may get biased results, especially for imprecise people. However, the error does not determine whether the measurement method is scientific or not. Engineering itself is a discipline that admits mistakes, and there are mistakes in metaphysics.

Mastering these points will not only make you more clearly understand that chassis performance is not metaphysics, but also help you to see whether a person pretends to understand and is mysterious.

Of course, the words are divided into two parts. Engineers are human beings, and they regard people as sensors. The accuracy is limited, there are many interference factors, the consistency is not good, and the persuasiveness will be worse. You said what you saw was black, and I said what I saw was white. What can you do? So is it possible for this thing to come out as "2 > 1"? Yes, but it's difficult. How difficult is it? We'll discuss it later. Welcome to continue to pay attention to Wonka Gong Hao.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.