How the variable valve timing system works

Variable Valve Timing Theory Reasonable selection of valve timing to ensure the best inflation efficiency HV is an extremely important technical issue to improve engine performance. Analyzing the working principle of the internal combustion engine, it is not difficult to conclude that in the four periods of intake and exhaust valve opening and closing, the change of the intake valve delay angle has the greatest impact on the inflation efficiency HV.

The relationship between the effect of the change of the intake valve delay angle on the charging efficiency, HV and engine power can be further illustrated in Figure 1. The HV curve of each inflation efficiency in Figure 1 shows the relationship between the HV of inflation efficiency and the rotation speed under a certain distribution timing. For example, when the closing angle is 40°, the inflation efficiency HV reaches the highest value at a speed of about 1800r min, indicating that the inertial inflation of the air flow can be best used to work at this speed.

When the rotation speed is higher than this speed, the airflow inertia increases, so that a part of the gas that could have been used to enter the cylinder by using the airflow inertia is locked out of the cylinder, and the speed increases, the flow resistance increases, so the inflation efficiency HV decreases. When the rotational speed is lower than this speed, the inertia of the airflow decreases, and at the beginning of the compression stroke, a part of the fresh gas may be pushed back into the inlet pipe, and the inflation efficiency HV also decreases. The relationship between the HV curves of different inflation efficiency and rotation speed under different distribution timing is reflected in the figure.

Different intake delay and closure angles are different from the maximum value of the inflation efficiency HV curve, and the general delay and closure angle increases, and the speed equivalent to the maximum value of the inflation efficiency HV curve also increases. Compared with the HV curve of inflation efficiency with a delay closure angle of 40° and a delay closure angle of 60°, the maximum equivalent rotational speeds of the curves are 1800 R min and 2200 R min, respectively. As the rotational speed increases, the airflow velocity increases, and the large tarding angle can make full use of the high-speed airflow inertia to increase inflation.

Changing the intake delay and closing angle can change the tendency of the HV curve of the charging efficiency with the change of speed, so as to adjust the engine torque curve to meet different use requirements. However, to be more precise, increasing the intake valve delay angle and increasing the inflation efficiency HV at high rpm are good for maximum power, but not for low- and medium-speed performance. Reducing the intake delay angle prevents the gas from being pushed back into the intake pipe, which helps to increase the maximum torque, but reduces the maximum power.

Therefore, the ideal valve timing should be adjusted in time according to the operating condition of the engine, and there should be a certain degree of flexibility. Obviously, for the traditional cam tappet valve train, it is difficult to meet the above requirements because it cannot be adjusted accordingly in the work, thus limiting the further improvement of engine performance. Application in the Passat B5 sedan Structure and transmission of variable valve timing The latest version of the Passat B5 sedan is a V6 engine, which is specially designed for variable valve timing.

From a top-down view, the transmission mode and the distribution of intake and exhaust camshafts are shown in Figure 2, where the exhaust camshaft is mounted on the outside and the intake camshaft is installed on the inside. The crankshaft is first driven by a toothed belt, and the exhaust camshaft is driven by a chain to the intake camshaft.

The mechanism and technology of automobile engine valve timing, also known as continuously variable valve timing system.

Variable valve timing system. This system is ubiquitous in today's high-performance engines. The system is equipped with a control and actuation system that adjusts the phase of the engine cam or valve spawn to optimize the engine valve process.

Because at high speed and low speed, the impact of the valve timing angle on the engine economy and power is obvious, and at high speed, the intake inertia can be fully utilized to improve the air intake volume and intake efficiency, so the valve opens early and closes late, and at low speed, on the contrary, most of the current engines have this technology.

The piston four-stroke engine is completed by four strokes: intake, compression, work and exhaust, and we are concerned about the degree of valve opening on the engine intake. The basic principle of cylinder intake is "negative pressure", that is, the difference in gas pressure between the inside and outside of the cylinder. When the engine is running at low speed, the degree of opening of the valve must not be too large, so that it is easy to cause the pressure inside and outside the cylinder to be equalized, and the negative pressure is reduced, so that the air intake is not sufficient. On the contrary, at high speeds, the speed is often 5000rpm, and if the valve is still shy and refuses to open, the intake of the engine will inevitably be blocked, so we need a long stroke of the valve lift.

Often, engineers want to take into account the torque characteristics of the engine in the low-speed area and the power characteristics of the high-speed area, so they can only adopt a "compromise" idea, and in the end, the engine has no power at high speed and lacks torque at low speed.

Therefore, in this case, there is a need for a device that adjusts the valve lift, which is what we call "variable valve timing technology". This technology can not only ensure high torque at low speed, but also obtain high power at high speed, which is a great breakthrough for the engine.

What are the advantages and disadvantages of variable valve timing technology and what are they? A lot of people don't know yet. Now let's take a look!

1.Variable valve timing technology: The crankshaft drives the camshaft to rotate through the toothed transmission device, so that the action of the valve when opening and closing forms a certain correspondence with the rotation angle of the crankshaft.

2.The gas flow rate varies with the engine speed, allowing the cylinder to achieve good intake efficiency at different speeds.

3.Therefore, it is necessary to change the opening and closing times of the valves. The oil pressure device must be installed at the front end of the camshaft so that when the rpm increases, the camshaft can turn at a small angle to open the intake valve as soon as possible.

1.Variable valve timing adjusts the phase of the engine's spike cam so that the amount of air changes with the engine speed. To a certain extent, the engine can achieve maximum combustion efficiency, improve fuel economy, fully burn fuel, and reduce carbon deposits.

2.Variable valve timing, also known as VVT, has the greatest effect on reducing NOx (nitrogen oxides) and HC (hydrocarbons) emissions, thereby increasing torque at low speeds and power burnout at high speeds. The variable valve timing structure is complex and has many parts, which is mainly composed of VVT solenoid valve, engine control computer, VVT phaser, sensor and oil circuit.

When the vehicle is driving normally on the road, the engine will also work with it, especially at high speeds, when the engine needs more air. However, on the basis of high rpm, the air required for the intake valve is completely closed before entering, resulting in a decrease in performance, so the timing of the opening and closing of the valve is important. Therefore, variable valve timing is the time to do its job.

It can adjust the overlap time and timing of the engine's intake and exhaust systems to speed up fuel combustion and improve efficiency.

The working principle of variable valve timing is that the phase of the engine cam is adjusted through the equipped control and execution system, so that the opening and closing time of the valve changes with the change of engine speed, so as to improve the efficiency of the inflation family fluid and increase the engine power.

The principle of VVT (Variab Le Valve Timing) is to adjust the amount of intake (exhaust), valve opening and closing time, and angle according to the operation of the engine. The amount of incoming air is optimal, and the combustion efficiency is improved. The advantage is fuel saving and the power-to-lift ratio is large.

The disadvantage is that the torque in the middle section is insufficient.

vvt means in Chinese"Variable valve timing", thanks to the electronic control unit (ECU) control, VVT-IThe system is the English abbreviation of Toyota's intelligent variable valve timing system, and the engines of most ** Toyota sedans have been generally installed with the VVT-i system. Toyota's VVT-i system continuously adjusts valve timing, but not valve lift.

Its working principle is: when the engine is converted from low speed to high speed, the electronic counter will automatically press the oil to the small turbine in the intake camshaft drive gear, so that under the action of pressure, the small turbine will rotate at a certain angle relative to the gear housing, so that the camshaft rotates forward or backward in the range of 60 degrees, so as to change the moment of opening the intake valve, and achieve the purpose of continuously adjusting the valve timing. (Photo by photo:.)

Zeng Caihong) @2019

When the engine starts.

When the stop pin of the variable valve timing actuator engages with the rotor, the camshaft sprocket rotates as a whole with the camshaft when the stopper pin is engaged with the rotor due to the spring force. When the pump pressure rises and the stop pin is disengaged, the corresponding angle between the camshaft sprocket and the camshaft can be adjusted.

Valve timing is advanced.

When the spool valve of the OCV moves to the left side following the PCM signal, the oil pump is hydraulically injected into the valve timing advance channel and finally reaches the valve timing advance chamber of the variable valve timing actuator. Then, together with the camshaft, the rotor rotates in the direction of valve timing advancement, the same direction of rotation as the crankshaft-driven casing, at which point the valve timing is advanced

Hello! The Variable Valve Timing System (VF) dynamically controls the opening and closing time and angle of the intake and exhaust valves of the engine according to the changes in engine speed and load to achieve the best valve timing. Its main functions include:

1.Improved fuel economy: By controlling the time and angle of valve opening, the optimal matching of engine suction and exhaust volume can be achieved, reducing stagnation loss and improving fuel economy.

2.Increased engine power and torque: The variable valve timing system enables the engine to achieve optimal intake and exhaust efficiency at different speeds and loads, resulting in higher power and torque.

3.Reduced emission pollution: The variable valve timing system can reduce the error of valve opening time, adjust the emission load, and reduce the emission oxygen content, thereby reducing the emission of harmful gases such as nitrogen oxides and carbon dioxide.

4.Improved driving comfort: By precisely controlling the opening time and angle of the valve, the valve impact noise and vibration can be reduced, and the stability and comfort of engine operation can be improved.

The function of valve variable dust timing is to control the opening time of engine valves, adjust the overlap time and timing (part or all) of the engine intake and exhaust system, reduce fuel consumption and improve efficiency.