Perspective on the intake control technology of th

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Automotive engine intake control technology perspective

automotive engine technology has made considerable progress since the advent of the car for more than 120 years. However, the real improvement of automotive engine technology has been in the past two decades, and these technological advances have benefited from the development of electronic computer technology

since the 1990s, the voice of environmental protection has become higher and higher, various countries pay more and more attention to the protection of the atmospheric environment, stringent environmental protection regulations have been issued, and vehicle emissions have become a prerequisite for entering the market; The decreasing oil resources have led to increasingly stringent requirements on vehicle fuel consumption; After entering the 21st century, these requirements are more stringent. Therefore, various automobile manufacturers do not hesitate to invest a lot of money in technical research, design and development. The use of computer simulation technology has greatly shortened the R & D and experimental cycle of new technology. Especially in recent years, with the continuous application of new materials, the progress of automobile engine technology can be said to be changing with each passing day, and there has been considerable progress. Except that the engine itself has not been greatly changed, other systems have undergone qualitative changes. Many ideas that were originally impossible in theory have become a reality today; Whether in terms of volume, mass, speed, power, stability or reliability, traditional engines and modern engines can hardly be compared

for a long time, the maximum output power and torque of the engine have been limited by the amount of air intake, so it is difficult to effectively improve it. The use of multi valve technology has solved this problem that has plagued engine designers for a long time to a certain extent. In recent years, through the efforts of automotive engineers in various countries, the intake control technology has been improved to a higher level, which is variable valve timing and variable intake system. This paper briefly talks about the new technological development of engine from the aspect of engine intake control

in cylinder intake airflow diagram of variable intake system

1. Variable valve timing:

also known as variable valve timing. During engine operation, there will be some contradictions that are difficult to solve under some working conditions, such as how to ensure torque output at low speed, power output at high speed and fuel consumption under these working conditions; It is difficult to successfully solve the problem if only the throttle controlled fuel supply mode is adopted! Now it can be effectively solved by means of variable valve timing and lift, variable intake duct and variable compression ratio. Typical examples are Toyota's variable valve timing control mechanism (VVT-i), Honda's variable valve timing Lift Electronic Control System (VTEC) and Saab's variable compression ratio technology

◆ Toyota Variable valve timing control mechanism (VVT-i): it can effectively improve the full load performance while maintaining the engine idle performance. It can keep the continuous opening angle of the inlet valve unchanged and change the opening and closing time of the inlet valve to increase the amount of inflation. It consists of three parts: VVT-i controller, camshaft timing oil control valve and sensor. The sensors include crankshaft position sensor, camshaft position sensor and VVT sensor

Toyota VVT-i 16 valve 4-cylinder engine

during operation, the exhaust camshaft is driven by the camshaft toothed pulley, and its angle relative to the toothed pulley remains unchanged. The crankshaft position sensor measures the crankshaft angle and provides the engine speed signal to the engine electronic control unit; Camshaft position sensor measures the angle of toothed pulley; The VVT sensor measures the angle of the inlet camshaft relative to the toothed pulley. Their signals are input to the engine electronic control unit (ECU), which controls the intake camshaft timing control valve according to the requirements of speed and load. The controller rotates the intake camshaft by an angle relative to the toothed belt according to the instruction, so as to achieve the purpose of delaying the opening and closing of the intake valve, so as to increase the intake delay angle at high speed, so as to improve the inflation efficiency of the cylinder

◆ Honda variable valve timing Lift Electronic Control System (VTEC): the VTEC system is controlled by the engine electronic control unit (ECU), which receives and processes the data and parameters of the engine sensors (including speed, intake pressure, vehicle speed, water temperature), outputs the corresponding control signals, and adjusts the rocker piston hydraulic system through the solenoid valve, so that the engine is controlled by different cams under different speed conditions, Affect the opening and time of the inlet valve

in general, each cylinder valve group of automobile engine is driven by only one group of cams, while the engine of VTEC system has two different groups of valves to drive cams with medium and low speed and high speed, which can be automatically converted through the intelligent control of electronic control system. It ensures the requirements of different valve timing and air intake at medium and low speed and high speed of the engine, so that the engine can achieve the unity and excellent state of power, economy and low emission no matter at any speed

◆ Saab variable compression ratio technology: generally, the compression ratio of engine cylinder cannot be changed, because the combustion chamber volume and cylinder working volume are fixed parameters, which have been determined in the design. However, in order to make the modern engine play a higher efficiency in various changing working conditions to improve the operating performance of the engine; Valve variable drive technology has been realized. Although some people have tried to change the important parameter of compression ratio from fixed to flexible in the past, changing the cylinder compression ratio will inevitably involve the change of the whole engine structure, which is very difficult. Therefore, this technological innovation has made very slow progress

the SVC engine developed by Saab can control the fuel consumption of the engine by changing the cylinder compression ratio. Its core is to install a wedge-shaped slider between the cylinder block and the cylinder head. The cylinder block can move along the slope of the slider, so that the relative position between the combustion chamber and the piston top surface changes, changing the volume of the combustion chamber, thereby changing the cylinder compression ratio. Its compression ratio can vary from 8:1 to 14:1. Adopt high compression ratio when the engine is under low load to save fuel; When the engine is under heavy load, a low compression ratio is used, supplemented by a supercharger to achieve high power and high torque output. SVC engine adopts 5-cylinder 1.6L displacement, cylinder diameter 68mm, stroke 88mm, maximum power 166kw, maximum torque 305nm, fuel consumption under comprehensive working conditions is 30% lower than that of conventional engine, and can meet the stringent European IV emission standard

2. Variable intake system:

to improve the dynamic performance of the engine, the only way to improve the inflation efficiency is to improve the inflation efficiency. In addition to supercharging, the appropriate valve timing can be adopted and can change with the engine speed, and the inertia and resonance effects of intake can also be used; These are the best ways to improve inflation efficiency. Intake inertia and resonance effect change with engine speed, intake pipe length and pipe diameter. At different speeds, the intake pipe length symptoms: the lower collet should be insensitive to rise and fall, so as to obtain a good intake inertia effect. Therefore, only combined with the variable valve timing control, the variable intake system can adapt to the requirements of different working conditions and comprehensively improve the engine performance

variable intake system is divided into two types: multi valve system and variable intake system; The purpose is to change the intensity of intake swirl and improve the inflation efficiency; Or to form resonance and intake pulse inertia effect, so as to meet the needs of improving performance under low-speed and medium high-speed conditions

◆ multiple valves are put into operation respectively: there are two ways for multiple valves to be put into operation respectively: one is to control the valves to open or close on time through cams or rocker arms; Second, a rotary valve is set in the airway to open or close the air inlet channel of the valve as required; The latter is simpler than using cam and rocker arm control

◆ variable inlet system: the variable inlet system uses intake pipes with different lengths and volumes to inflate the cylinder according to different working conditions of the engine, so as to form inertia inflation effect and resonance pulse wave effect, so as to improve inflation efficiency and engine power performance. It has three working forms: double pulse intake system, four valve two-stage intake system and three-stage intake system

(1) the centralized commencement ceremony of key projects of Suining City in the second quarter of 2017 was held in Shehong County of the city: the double pulse intake system is composed of an air chamber and two pulse intake pipes. A throttle is set at the inlet of the air chamber, which is connected with two intake pipes with larger diameters. Its function is to prevent the mutual interference of resonant air columns in the intake pipes of two groups (one group per three cylinders). Each pulse tube becomes a channel to form a resonant air wave, which is connected to two groups of cylinders respectively. The intake ports of the six cylinder engine are divided into front and rear groups, which is equivalent to the intake pipes of two three cylinder engines. Each cylinder has a 240 ° intake stroke, and there will be no interference between the intake pulses. The system can make each cylinder produce the dynamic effect of air resonance wave, and the air chamber with larger diameter and the channel in the middle that produces resonance air wave together with the manifold form a pulse wave resonance cycle system. Its work is divided into two sections: the low-speed section (speed 4400r/min)

(2) four valve two-stage intake system: the second stage is the low and medium speed stage (speed 3800r/min); The intake system is connected with the air chamber by a long curved intake pipe and a short straight intake pipe, which are respectively connected to the two intake valves of the cylinder head. Under the low and medium speed working conditions of the engine, the power valve closes the channel of the short air inlet pipe, and the air is supplied to the cylinder through the long curved air channel, which increases the air flow speed and forms a strong vortex to promote the formation of a good mixture. In high-speed working conditions, the power valve is opened, and additional air enters the cylinder from the air chamber through the short air inlet pipe, which improves the volumetric efficiency. The air flow entering the cylinder from another valve changes the vortex formed in low and medium speed working conditions into tumble motion, which can better meet the needs of improving combustion at high speed and high load. It can improve the inflation rate of the cylinder and realize the purpose of improving the dynamic performance of the engine. In addition, the length of the intake pipe can form a strong reflection pressure peak when the intake valve is about to close, increasing the amount of air entering the cylinder. This helps to improve the torque of the engine at low speed

(3) three section air intake system: three sections, namely, low-speed section (speed 4000r/min) and high-speed section (speed>5000r/min); Unlike the two-stage air intake system, it is composed of two air chamber pipes connected at the ends and arranged between V-shaped included angles. Each air chamber is connected to the left or right cylinder through three separate pulse tubes. Each side of the cylinder forms an independent three cylinder engine, and the intake stroke phase of each cylinder is evenly separated by 240 °. There are respective throttle valves at the inlets of the two air chambers. There is a connecting channel controlled by the valve in the middle of the two air chambers. Two butterfly valves are arranged at the U-shaped connecting pipe at the end of the air chamber. Under the low-speed working condition of the engine, the valve between the two air chamber pipes and the high-speed working condition are closed by the valve. Each air chamber pipe and the three pulse intake pipes connected to it form a complete resonance system, which will integrate the inertia and fluctuation effects under a certain speed condition (speed = 3500r/min), so that the inflation efficiency and torque reach the peak

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