Text/Qin Ming
Earlier we talked about an engine circulation technology article, which mentioned the early opening and late closing of the intake valve. So how? It is achieved through variable timing valve technology, which is the well-known VVT technology.
Variable timing valve technology, which can be read literally, is to control the opening time of the valve during the routine operation of the engine. However, the VVT technology of each car company is not the same, some VVT structure is very complex, but the fuel saving effect is not too obvious, and some structures are very simple, but can greatly improve the engine power, fuel consumption is greatly reduced.
Although the name is various, but the principle remains unchanged, it is the valve timing, so as to control the amount of air inhaled by the intake valve, to achieve the effect of improving performance and saving fuel consumption, this time we take the well-known Toyota VVT-i to do the following example.
The VVT-i system consists of sensors, ECUs and camshaft hydraulic control valves, controllers and other parts. The ECU stores the best valve timing parameter values, crankshaft position sensors, intake manifold air pressure sensors, throttle position sensors, water temperature sensors and camshaft position sensors and other feedback information is collected into the ECU and compared with the predetermined parameter values, the calculated parameter information is calculated and issued instructions to the hydraulic control valve, the position of the oil tank valve is controlled.
It can be seen through the structure that the exhaust valve and the intake valve are both top pressure exhaust valves by camshafts, so if you want to control the exhaust and intake switch time, you need to control the camshaft, mainly by controlling the angle of the cam to achieve, when one side of the cam comes into contact with the valve, start to prepare to squeeze the valve top rod downward movement, with the rotation of the camshaft, the cam also begins to rotate, the valve valve continues to move downwards, causing the valve valve to open, rotate to the most protruding point of the cam structure, reach the maximum degree of opening, and then continue to rotate, The force of the cam on the valve ejector rod is also reduced, and the valve valve begins to move back until the cam bulge part is turned, the valve top bar is no longer squeezed, and the valve valve is completely closed.
That is very simple way to change the angle of the cam to achieve, control the valve switch time, the larger the angle of the cam contact time, the earlier the valve opening time.
It is also possible to control the opening time of the valve valve by controlling the rotation time of the camshaft, which requires sensors and phasers to make variable adjustments to the camshaft, the intake camshaft and the exhaust camshaft are mainly driven by a timing chain, the timing chain is used to drive, one end is connected to the engine crankshaft sprocket, a section is connected to the phaser, and the engine crankshaft rotates to drive the phaser, so that the camshaft begins to rotate. The focus of VVT technology is the phaser, the outer wheel of the phaser is connected to the sprocket, the inner wheel and the cam are connected, and there are two oil chambers between the two wheels, one to control the valve to open early, and one to control the valve to delay closing.
The crankshaft position sensor can identify the angle of the current camshaft, check the state of the camshaft, calculate the opening time and closing time of the valve through the controller, and then transmit the signal to the solenoid valve to control the amount of oil in the two oil chambers, and the difference in oil volume leads to a pressure difference between the two wheels, so that the relative position of the inner and outer wheels rotates, so that the rotation time of the camshaft can be controlled.
The uniqueness of Toyota VVT-i technology is that ECM automatically searches for an optimal valve timing corresponding to engine speed, intake capacity, throttle position and cooling water temperature under various driving conditions, and controls the camshaft timing hydraulic control valve, and senses the actual valve timing through the signals of each sensor, and then performs feedback control to compensate for system errors and achieve the best valve timing position, so as to effectively improve the power and performance of the car, minimize fuel consumption and exhaust emissions.
Although VVT technology has different differences in various manufacturers, there are VVT, VVT-i, VVT-W, DVVT, CVVT and other scenes of flowers, which can bring a better experience to consumers, which is also what consumers are happy to see.