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Whether an engine is advanced or not depends largely on it

Source: Xinxin Used Cars Release time: 2018-03-15 20:20:00 Views:

How to judge whether an engine is good? In addition to looking at horsepower and torque, we will also see that this engine runs smoothly and steadily, and the noise is not large. These are easily distinguishable without any professional knowledge.

As usual, the smoother an engine, the lower the noise, and the higher the nature. But where do these vibration noises come from? What affects the vibration and noise of the engine?

About vibration

一台发动机高级与否 很大程度就看它

There must be vibrations when the engine is running, which everyone knows. But where does the vibration come from? How does vibration affect the engine?

This seemingly simple question is complicated to answer. In fact, in the university of Huangjiang used automobile dealership in the automobile industry of Dongguan, there are dozens of books on engine vibration alone. Due to space limitations, we cannot provide a complete introduction for everyone, so we only introduce engine vibration The two most basic concepts: first-order vibration and second-order vibration.

Some basic theories before starting

Before the official start, we need to know some basic things. First of all, the used automobile engine of Huangjiang Automobile in Dongguan is a four-stroke engine. The piston moves up and down four times. The spark plug is fired once and the work is done once. The piston is connected to the crankshaft through the connecting rod. That is, each time the piston moves from top to bottom (or vice versa), the crankshaft rotates 180 degrees. It's very simple, I believe everyone understands it, and then start to study the first-order vibration.

First-order vibration

First of all, we carefully analyzed the impact of each piston's embarrassment on the crankshaft.

The first is suction and compression. The piston is not subject to much force. The crankshaft pulls the piston up and the piston reaches the top dead center. The ignition explodes and the piston is pushed down. This will cause an axial tilt of the crankshaft. The large downward vibration, the piston continues to run, and the vibration in the same direction continues to accumulate, and the entire engine body will tremble violently along the way. This is why the single-cylinder engine is so vibrating so much.

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In order to solve this problem, engineers can only equip the engine with more cylinders. Between the multiple cylinders, due to the difference in the relative position of the crankshaft, the balance of forces in a certain direction will be formed. how to say? We further analyze the stress state of the crankshaft.

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The picture above is a crankshaft. When a cylinder does work, it will generate a force module power at one end, and the adjacent cylinder will be in the opposite position to the previous cylinder, that is, it will generate a commensurate force at the other end of the crankshaft. These forces are all The bearing at the center of the connection between the two cylinders of the crankshaft is subjected to the force of this bearing. We call it the rotating torque.

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Of course, the rotating torque generated between adjacent cylinders has a direction. This directional vibration, plus the vibration caused by the up and down movement of the piston, is called first-order vibration.

To offset the first-order vibration, you can only offset online marketing promotion by generating a rotating torque with the opposite force in the same direction. If the first-order vibration can be offset, we must arrange at least 4 cylinders on a unified crankshaft, which everyone knows. Inline 4-cylinder machine.

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For the inline 3 cylinder, because it cannot complete the offset, a large-weight balance shaft is required to do the inline 4 cylinder. Therefore, the inline 3 cylinder has a gap with the inherently balanced inline 4 cylinder.

Second-order vibration

The in-line 4-cylinder solves the first-order vibration, but what it cannot solve is the second-order vibration. Among engine vibrations, first-order vibration accounts for 70% and second-order vibration accounts for 30%. But what does second-order vibration mean?

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Interpreting second-order vibrations is a bit complicated, so you need to use a little space thinking ability. We first disassemble the piston-connecting rod-crankshaft system separately for interpretation.

The piston is connected to the connecting rod and the connecting rod is connected to the crankshaft. The piston runs up and down and rotates with the crankshaft. But slow! Here comes the question. Is the distance of piston movement the same as that of crankshaft?

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Not the same, we open the rotation of the crankshaft to a straight line, and then compare with the piston connecting rod, we will find that the piston runs significantly faster than the crankshaft. Therefore, returning to the previous step, the difference in speed between the two personnel examination centers in Xinjiang will cause vibration at the crankshaft journal, which is second-order vibration.

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So how to solve the second-order vibration?

There is only one way: insert as many cylinders as possible in one crankshaft, and the number of cylinders must be even. Therefore, the inline 6 cylinder recommended by BMW is significantly better than the inline 4 in terms of ride comfort and noise. The reason is that the inline 6 not only cancels the first-order vibration, but also the second-order vibration.

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