Air intake system

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The air intake system is composed of Air filter 、 Air flow meter 、 Intake pressure sensor 、 Throttle Body , additional Air valve 、 Idle speed control valve , resonant cavity, power cavity Intake manifold Etc.

Chinese name: Air intake system
Foreign name: intake system

Composition: By air filter and air flow meter
Classification: Variable intake system
Application model: Beijing Hyundai Elantra

catalog

three classification
four Application model
five Variable gas distribution technology
six Intake system noise

brief introduction

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Intake system structure

Figure 1 is a schematic diagram of the air intake system. A complete intake system can be divided into two parts: the engine intake manifold manifold system and the air intake system. Air inlet system - the system includes air inlet control valve, idle air inlet channel, bellows hose, clean air pipe, 1/4 wavelength pipe, air filter, filter element, resonance chamber, air inlet pipe, etc.^[1]

Function of air intake system

Figure 1

The main function of the air intake system is to deliver clean, dry, sufficient and stable air for the engine to meet the needs of the engine, and to prevent impurities and large particles of dust in the air from entering the engine combustion chamber to cause abnormal engine wear. Another important function of the air intake system is to reduce the noise. The air intake noise not only affects the passing noise of the whole vehicle, but also affects the noise inside the vehicle, which has a great impact on the riding comfort. The intake system design directly affects the power and noise quality of the engine and the ride comfort of the whole vehicle. The reasonable design of noise elimination components can reduce the noise of subsystems, and thus improve the NVH performance of the whole vehicle.^[2]

working principle

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When the engine is working, the driver passes Accelerator pedal control Solar term door To change the opening of Intake volume To control the operation of the engine. The air entering the engine passes through Air filter After filtering out dust and other impurities Air flow meter , enter the power chamber along the throttle passage Intake manifold Assigned to each Cylinder Medium; Engine cold idling During operation, some air passes through the additional air valve or Idle speed control valve Bypass the throttle valve and enter the cylinder.

classification

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The modern automobile intake system is mainly variable intake system. Variable intake system is mainly divided into VVT（ Variable valve timing ）， CVVT (continuously variable valve timing), VVT-i (electronic variable timing), i-VTEC (Electronic variable valve lift).

Application model

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The four main application models of variable intake system are:

Beijing Hyundai Elantra ：VVT（ Variable valve timing ）；

Dongfeng Yueda Kia cerato ： CVVT (Continuous variable valve timing);

Toyota vehicle series, such as Carola 、 Corolla VVT-i (Electronic variable timing);

Honda Vehicle series, such as Accord 、CRV、 civic i-VTEC (Electronic Variable valve Lift);

BYD Vehicle series, such as 2012 model F3 G3, L3 VVL (variable valve lift).

Variable gas distribution technology

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Variable gas distribution technology, divided into categories, including Variable valve timing And variable valve travel.

First, let's talk about common Engine valve train It is known that the valve is passed by the crankshaft of the engine Camshaft Driven, the valve timing depends on the angle of camshaft. When the engine is running, we need to let more fresh air enter combustion chamber The best solution is to let the intake valve open in advance and let the exhaust valve close later so that the exhaust gas can be discharged from the combustion chamber as much as possible. In this way, between the intake stroke and the exhaust stroke, the intake valve and the exhaust valve will open at the same time. This overlap between the intake and exhaust valves is called the valve overlap angle. On an ordinary engine, the opening and closing time of the intake valve and exhaust valve are fixed, and the valve superposition angle is also fixed, which is the best obtained according to the test Valve timing , which cannot be changed during engine operation. however engine speed High and low to inlet, exhaust flow and Cylinder The internal combustion process is influential. When the rotating speed is high, the flow rate of the intake air flow is high and the inertia energy is large. Therefore, it is hoped that the intake valve will be opened earlier and closed later so that the fresh air can be smoothly filled into the cylinder and as much mixture or air as possible. On the contrary, when the engine speed is low, the intake flow rate is low and the flow inertia energy is small. If the intake valve is opened too early piston The positive upward exhaust can easily squeeze the fresh air out of the cylinder, making the intake air less and the engine unstable. Therefore, there is no fixed valve superposition angle setting that can make the engine output perfectly at high and low speed Variable valve timing technology The engine can only select the optimized fixed valve superposition angle according to the requirements of its matching vehicle model. For example, the engines of racing cars generally use smaller valve superposition angles to facilitate the power output at high speeds. While ordinary civil vehicles use moderate valve superposition angle, taking into account the power output at both high speed and low speed, but will lose a lot of power at low speed and high speed. The variable valve timing technology is to solve this contradiction by means of technical means to realize the variable valve superposition angle.

For example, in the early 1990s, Honda introduced a new type of valve that can change both the valve timing and valve movement Variable valve timing - The lift control mechanism is the first valve control system in the world that can simultaneously control the valve opening/closing time and lift. That's what we all know now VTEC Mechanism: general engine per cylinder Valve block It is driven by only one set of cams, while VTEC system However, our engine has two different sets of valves to drive cams, which are used for medium and low speed and high speed, and can be automatically switched through the automatic control of the electronic control system. use VTEC system , which ensures that the engine is different in medium and low speed and high speed Valve timing and Intake volume To make the engine meet the requirements of Power , economy and low emissions are unified and in excellent condition. It should be noted that the engine adopts Variable valve timing While the technology gains the above benefits, there is no negative impact. In other words, there is no higher requirement for the working intensity of the engine.

VTEC is designed as if two different Camshaft Yes, one for low speed and one for high speed, but VTEC engine The difference is that the two camshafts are designed on one camshaft.

In the intake camshaft of Honda engine, apart from a pair of cams (main cam and secondary cam) and a pair of cams that control two valves rocker arm In addition to (main rocker arm and secondary rocker arm), a higher intermediate cam and corresponding rocker arm (intermediate rocker arm) are also added. The three rocker arms are equipped with small hydraulic control moving arms piston 。

When the engine is at low speed, the small piston is in the original position, and the three rocker arms are separated. The main cam and the secondary cam push the main rocker arm and the secondary rocker arm respectively, controlling the opening and closing of the two inlet valves. The valve lift is less, which is like an ordinary engine.

Although the middle cam also pushes the middle rocker arm, because the rocker arms are separated, the other two rocker arms are not controlled by it, so the opening and closing status of the valve will not be affected. When the engine reaches a set high speed, the computer will command the solenoid valve to start the hydraulic system to push rocker arm The small piston inside makes the three rocker arms locked together and driven by the middle cam c. Since the middle cam is higher than other cams and has a large lift, the opening time of the inlet valve is extended and the lift is also increased. When the engine speed decreases to a certain set low speed, the hydraulic pressure in the rocker arm also decreases, the piston returns to its original position under the action of the return spring, and the three rocker arms are separated.

whole VTEC system It is controlled by the engine electronic control unit (ECU) and received by the ECU Engine sensor (including speed, intake pressure, vehicle speed, water temperature, etc.), output corresponding control signals, and adjust rocker arm through solenoid valve piston Hydraulic system, so that the engine is controlled by different cams under different speed conditions, affecting the opening and time of the inlet valve.

Honda Of VTEC engine The technology has been introduced for about ten years, and the fact also proves that this design is reliable. It can improve the performance of the engine at various speeds, whether at low speeds Fuel economy And operation Ride comfort Or acceleration at high speed. It can be said that the electronic control valve mechanism replaces the traditional Cam mechanism Previously, Honda's VTEC Technology can be said to be a good method.

Intake system noise

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influence factor

The noise of air intake system is one of the most important noise sources of automobiles. It is of great significance to control and optimize it. The intake noise is caused by the pressure fluctuation caused by the periodic opening and closing of the intake valve and the high-speed airflow passing through the intake valve channel during the intake process. According to the different generation mechanisms, the intake noise mainly includes the following: periodic pressure fluctuation noise, vortex noise, Helmholtz resonance noise of the cylinder and cylinder resonance noise of the intake pipe; Air filter The wall panel of Helmholtz muffler is very thin. When the high-speed airflow passes through, it is easy to be excited and cause radiated noise. The acoustic performance of the air intake system is affected by such factors as the silencing volume, the cross-sectional area of the pipe, and the position of the intake pipe orifice.^[3]

Noise reduction measures for air intake system

The treatment methods of gas flow noise and structure noise are relatively simple, and they are often not the main noise of the intake system. This paper mainly discusses the noise reduction measures of low-frequency noise.

(1) Reasonable design Air filter 。 Generally speaking, the greater the noise reduction volume, the better the noise reduction effect. However, it is also necessary to comprehensively consider the layout space, part weight and part cost factors. Generally, the volume of the air filter is more than 3 times of the engine volume, which can achieve good sound attenuation effect.

(2) Determine the inlet and outlet pipe diameter and length of the air filter. Reducing the inlet and outlet pipe diameters of the air filter and increasing the expansion ratio are conducive to reducing noise, but will lead to an increase in the resistance of the intake system, reduce the intake volume of the engine engine performance 。 The effective noise elimination frequency of the air filter is related to the length of the intake pipe. If the length of the intake pipe is increased, the effective noise elimination frequency of the air filter will move to the low frequency, so it is necessary to design the length of the inlet and outlet pipes reasonably.

(3) Reasonably design silencing elements. Commonly used silencing elements include resonant cavity, 1/4 wavelength tube, porous tube, braided tube, etc. Resonant cavity is generally aimed at low frequency, 1/4 wavelength tube is generally used to eliminate middle and high frequency noise, and porous tube and braided tube are mainly used to eliminate noise with wide frequency band.^[2]

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