At present, the mainstream of VVT system is transverse OCV VVT system, which is mainly composed of phase modulator and OCV oil control valve. Auxiliary components include camshaft phase sensor, crankshaft phase sensor, ECU, camshaft signal wheel, crankshaft signal plate, check valve, VVT center bolt, etc.
The phase modulator is the actuator that finally adjusts the valve timing. Its basic structural principle is that each oil chamber of the phase modulator contains two hydraulic chambers, a valve timing advance chamber and a valve timing delay chamber. These two hydraulic chambers are located between the camshaft sprocket support housing and the camshaft rotor connected to the camshaft. The oil pump supplies oil for these two rooms. The oil control valve (OCV valve) controls the hydraulic level of the two chambers, and adjusts the relative phase between the camshaft sprocket and the rotor according to the engine working conditions. Because the rotor is connected with the camshaft, the phase of the throttle valve is also adjusted to obtain the best valve distribution effect.
Lock pin: The function of the lock pin is that after the engine is turned off, the phase modulator returns to the initial position, and the lock pin falls under the action of the spring to fix the initial phase of the phase modulator. After the engine is ignited and the oil pressure is restored, the lock is released so that the phase modulator can freely adjust the phase. ?
Because of the high matching precision between the lock pin and the lock pin hole and the speed requirement of VVT adjustment, we must fix the rotor position of a VVT before locking and unlocking, otherwise the rotor is in a free state, and it is difficult for the lock pin to be inserted into the lock pin hole. As can be seen from the physical drawing on the right side of the above figure, it is generally necessary for the rotor to lean against one side of the stator oil chamber and the relative position of the rotor and stator is fixed to unlock the lock pin. However, when the rotor leans against one side of the stator oil chamber, the valve timing must be in the position of maximum advance or maximum lag, which is also the initial phase of VVT. Therefore, generally speaking, the phase modulator can only be adjusted from the initial position to the maximum leading direction or the maximum lagging direction, that is, it can only be adjusted from the initial phase to one direction. This limits the strategic application of VVT, and the initial stage can only be placed in a compromise position, which can cover the required stage of this engine as much as possible, but this position is generally not the optimal start/cold start stage, and strategic optimization calibration is needed. Of course, the intermediate locked phase modulator can solve this problem. We'll talk about intermediate locked phase modulators next time.