Structure and working principle of variable intake manifold

Variable intake manifold improves combustion efficiency by changing the length and cross-sectional area of intake pipe, which makes the engine more stable at low speed, more abundant torque, smoother at high speed and more powerful. Variable intake manifold structure (Figure) Variable intake manifold (Volkswagen Magotan) 1- air temperature sensor bolt; 2- Air temperature sensor; 3- activated carbon canister solenoid valve; 4- intake pipe; 5- vacuum tank; 6— High-pressure pump bolts; 7 —— Connecting joint of fuel pipeline of fuel tank; 8— Fuel pressure regulating valve; 9- Mechanical single-piston high-pressure pump; 10- shaft sleeve; 1- The connecting pipe (accumulator) is connected to the fuel pipeline of the fuel distributor; 12- inlet flap control valve; 13-injection valve; 14- intake pipe connector; 15- intake pipe joint bolt; 16- fixing nut of air inlet pipe joint; 17- Throttle control unit bolt; 18- throttle control unit; 19 —— Working principle of variable intake pipe with sealing ring. One end of the intake manifold is connected to the intake valve, and the other end is connected to the intake resonance chamber behind the intake manifold. Each cylinder has an intake manifold. When the engine is running, the intake valve is constantly opened and closed. When the valve is opened, the mixture in the intake manifold enters the cylinder through the valve at a certain speed. When the valve is closed, the mixture will rebound when it is blocked, and the vibration frequency will be generated repeatedly. If the intake manifold is short, obviously this frequency will be faster; If the intake manifold is long, this frequency will become relatively slow. If the oscillation frequency of the mixture in the intake manifold vibrates with the opening time of the intake valve, it is obvious that the intake efficiency is high. Therefore, the variable intake manifold can provide optimal air distribution at high and low engine speeds. When the engine is running at low speed, the intake speed and air pressure intensity can be improved by using the slender intake manifold, which makes the gasoline atomization better, combustion better and torque increased. Just like squashing a water pipe, the current will be stronger. The engine needs a lot of mixed gas at high speed, which makes the intake manifold thicker and shorter, so that more mixed gas can be inhaled and the output power can be improved. Technical principle of variable intake manifold Because the mixture is a fluid with mass, the flow state in the intake pipe is ever-changing. In engineering, fluid mechanics is often used to optimize its internal design, such as grinding the inner wall of intake manifold to reduce the resistance, or deliberately making rough surfaces to create eddy current movement in the cylinder. However, the working speed range of automobile engine is as high as several thousand revolutions, and the intake demand required for each working condition is different, which is a great test for ordinary intake manifold. As a result, engineers developed the intake manifold deeply, which changed the intake manifold. The variable-length four-stroke engine can complete a working cycle only when the piston reciprocates up and down twice, and the intake valve only opens for 1/4, thus generating intake pulse in the intake manifold. The higher the engine speed, the shorter the valve opening interval and the higher the pulse frequency. Simply put, the greater the vibration of the intake manifold. Engineers improve the airflow by changing the length of the intake manifold. The intake manifold is designed in a spiral shape and distributed in the middle of the engine block, and the airflow enters from the middle. When the engine is running at a low speed of 2000 rpm, the black control valve is closed and the airflow is forced to enter the cylinder from the long manifold. At this time, the natural frequency of the intake manifold is reduced to adapt to the low speed of air flow. When the engine speed rises to 5000 rpm, the intake frequency rises. At this time, the control valve is opened, and the airflow bypasses the downcomer and is directly injected into the cylinder. This reduces the * * * vibration frequency of the intake manifold, which is beneficial to high-speed intake. Variable cross-section We know that at low speed, the valve will be set to short-stroke opening, and at high speed, the valve will be set to long-stroke opening, all of which are caused by negative pressure. So can't the intake manifold achieve the same effect except the valve? According to the principle of fluid mechanics, the larger the cross-sectional area of the pipeline, the smaller the fluid pressure; The smaller the cross-sectional area of the pipeline, the greater the fluid pressure. For example, when we were young, we all played with tap water, the front end of the water pipe, and the pressure w of tap water. According to this principle, the engine needs a mechanism to improve the intake flow by using the larger cross-sectional area of the intake manifold at high speed; Using a smaller cross-sectional area of the intake manifold at low speed can improve the intake negative pressure of the cylinder, and can also fully form a vortex in the cylinder, so that air and gasoline can be better mixed. Variable intake manifold function The variable-length intake manifold system adjusts the length of the intake manifold according to the engine speed. When the engine speed is low, it is adjusted to a longer intake manifold. According to the vibration principle, when the length of the intake manifold becomes longer, its natural frequency will decrease, which is close to the vibration frequency of the low-speed airflow at this time, resulting in the * * * vibration effect, which makes the intake air of the engine increase at low speed and obtain greater torque. However, at high speed, due to the long intake pipe, the intake throttle resistance is large and the maximum output power decreases. Therefore, when the engine speed is high, it is adjusted to a shorter intake manifold to increase its natural frequency, which is close to the vibration frequency of high-speed airflow at this time, and it also produces a * * vibration effect, which increases the intake air volume of the engine at high speed and makes the engine gain more power. The structural principle of the variable-length intake manifold system is shown in Figure 1. It is mainly composed of an intake pipe changeover valve and an intake pipe changeover valve control mechanism. The control mechanism of intake pipe switch valve includes ECU, intake pipe switch vacuum solenoid valve, intake pipe switch vacuum diaphragm box, vacuum actuator and other components. Variable intake pipe length and variable intake manifold length are widely used in ordinary civil vehicles. The length of most intake manifolds is divided into two sections, and the length can be adjusted to 33,354 at low speed and to a short intake manifold at high speed. It should be easy to understand why it should be designed as a short intake manifold at high speed, because it can make the intake more smooth. But why do you need a long intake manifold at low speed? Won't it increase the intake resistance? Because the intake frequency of the engine at low speed is also low, the long intake manifold can gather more air, so it is very suitable to match the intake demand of the engine at low speed, thus improving the torque output. In addition, the long intake manifold can also reduce the air flow, make the air and fuel mix better, burn more fully and produce greater torque output. This form is the most common. Variable intake resonance is used to improve the power of the engine at medium and high speed through intake resonance. Each cylinder uses the same vibration chamber, two of which are connected with each other. One of the intake pipes can be opened and closed by a valve under the control of ECU. This valve switching frequency is related to the intake frequency between cylinders (the intake frequency actually depends on the engine speed). In this way, a pressure wave is formed between cylinders. If the intake frequency is symmetrical with the rotational speed of the pressure wave, according to the principle of * * * vibration, air will be forcibly pushed into the cylinder due to strong * * * vibration, thus improving the principle of changing the intake efficiency: the frequency of the pressure wave is controlled by staggered intake pipes, and one of them is closed at low rotational speed, so that the frequency of the pressure wave is reduced and coincides with the relatively low intake frequency, thereby improving the torque output at medium and low rotational speed; On the contrary, at high speed, the valve opens, so many high-performance new cars also adopt variable exhaust back pressure technology. Similar to the variable intake manifold technology, the variable exhaust back pressure technology is only designed for exhaust gas. The exhaust pipe of a common sports car collects the exhaust gas from a single cylinder and collects it in the exhaust manifold, forming a new exhaust pulse and forming reverse pressurization. Reverse supercharging can only play its best role when the engine is at a certain speed, and the length of the exhaust pipe determines its applicable speed range. The short exhaust pipe is suitable for low-speed pressurization, while the long exhaust pipe is the opposite. For the engine with fixed exhaust pipe length, it can only be designed to be the most suitable for the relatively compromised variable exhaust pipe length technology. Using two exhaust pipes with different lengths, you can pass through the opening and switch with each other.