Variable valve timing system. Now N/A (naturally aspirated) engine technology is adopted. The system adjusts the phase of the engine cam through the equipped control and execution system, so that the opening and closing time of the valve changes with the change of the engine speed, thus improving the charging efficiency and increasing the engine power.

The principle of VVT (Variable Valve Timing) technology is to adjust the intake (exhaust) amount, valve opening and closing time and angle according to the engine operation. It is to optimize the air intake and improve the combustion efficiency. Its advantages are fuel saving and high lift ratio. The disadvantage is the lack of speed and torque in the middle section.

The VVT of Korean cars is based on the VVT-I of Toyota in Japan and the VTEC technology of Honda. However, compared with Toyota's VVT-I variable timing valve technology, VVT is only a variable valve technology and lacks timing technology, so VVT engine is indeed more fuel-efficient than ordinary engines, but not as fuel-efficient as Toyota and Honda cars of Japanese cars.

In fact, Volkswagen's sagitar 1.6-liter 2-valve engine also has variable valve phase technology, but it is not as good as advertised by Japanese cars and Korean cars. But as far as engine technology is concerned, the engines of Japanese cars are not more advanced than those of German cars. Many people think that Japanese cars save fuel because their engines are advanced. In fact, this is a misunderstanding.

BMW has adopted this technology in the previous generation engines, such as Honda's VTEC, i-VTEC,; Toyota's vvt-I; Nissan's CVVT；; ; Mivik; Mitsubishi; Suzuki's VVT；; ; Modern VVT；; ; Kia's CVVT has gradually started to be used. Generally speaking, it is actually a technology with different names.

VVT - i

VVT means "variable valve timing" in Chinese. Because it is controlled by electronic control unit (ECU), Toyota has a nice Chinese name "Intelligent Variable Valve Timing System". The system mainly controls the camshaft of the intake valve, and has a small tail "I", which is the English code for "intake". These are the literal meanings of "vvt-I". VVT-I system is the abbreviation of Toyota Intelligent Variable Valve Timing System, which has been widely installed in the latest Toyota engine. Toyota's VVT-I system can continuously adjust the valve timing, but it cannot adjust the valve lift. Its working principle is that when the engine changes from low speed to high speed, the electronic computer automatically presses the engine oil to the small turbine in the driving gear of the intake camshaft, so that the small turbine rotates at a certain angle relative to the gear box under the pressure, and the camshaft rotates forward or backward within 60 degrees, thus changing the opening time of the intake valve and achieving the purpose of continuously adjusting the valve timing.

VVT-I is a device to control the valve timing of intake camshaft. By adjusting the valve timing of camshaft angle, the power and fuel economy of the engine in all speed ranges are improved and the exhaust emission is reduced.

VVT-I system consists of sensor, ECU, camshaft hydraulic control valve and controller. The ECU stores the optimal valve timing parameter values, and feedback information such as crankshaft position sensor, intake manifold pressure sensor, throttle position sensor, water temperature sensor and camshaft position sensor is collected in the ECU and compared with the predetermined parameter values to calculate the correction parameters and send instructions to the hydraulic control valve to control the camshaft timing. The control valve controls the position of the oil pan valve according to the instruction of ECU, that is, changes the hydraulic flow, and selectively sends signal instructions such as advance, delay and invariability to different oil circuits of VVT-I controller.

According to the installation position of the controller, VVT-I system can be divided into two types. One type is installed on the exhaust camshaft, which is called vane VVT-I, and Toyota Previa installed this type. The other is installed on the intake camshaft, called spiral groove VVT-I, and installed on Toyota Lexus 400, 430 and other advanced cars. Their structures are somewhat different, but their functions are the same.

The vane VVT-I controller consists of a housing driving the intake camshaft and an impeller connected to the exhaust camshaft. The oil pressure from the leading or lagging oil passage is transmitted to the exhaust camshaft, which makes the shell of VVT-I controller rotate, drives the intake camshaft and continuously changes the intake timing. When the oil pressure is applied to the advance side oil chamber rotating housing, the intake camshaft rotates in the advance direction; When the oil pressure acts on the rotating housing of the oil cavity on the lagging side, the intake camshaft rotates in the lagging direction; When the engine is stopped, the camshaft hydraulic control valve is in the maximum lag state.

The spiral groove VVT-I controller includes a gear driven by a timing belt, an internal gear rigidly connected with the intake camshaft, and a movable piston located between the internal gear and the external gear. There are spiral splines on the surface of the piston, and the piston moves along the axial direction, which will change the phase of the internal gear and the external gear, thus causing the continuous change of the valve distribution phase. When the oil pressure is applied to the left side of the piston, forcing the piston to move to the right, the intake camshaft will advance by a certain angle relative to the camshaft timing pulley due to the helical spline on the piston. When the oil pressure acts on the stone side of the piston, forcing the piston to move to the left, it will delay the intake camshaft by a certain angle. When the ideal valve timing is obtained, the camshaft timing hydraulic control valve will close the oil passage to balance the pressure on both sides of the piston and the piston will stop moving.

Now all advanced engines have "Engine Control Module" (ECM), which is responsible for ignition, fuel injection, emission control, fault detection and so on. The ECM of Toyota VVT-I engine automatically searches for the optimal valve timing corresponding to engine speed, air intake, throttle position and cooling water temperature under various driving conditions, and controls the camshaft timing hydraulic control valve. The actual valve timing is sensed through the signals of various sensors, and then feedback control is carried out to compensate the system error and reach the optimal valve timing position, thus effectively improving the power and performance of the automobile and minimizing the fuel consumption and exhaust emissions.