Valve Overlap Angle on The Influence of The Engine
When the engine at high speed interval, four stroke engines a work only a few seconds to per stroke, such a short time often can cause lack of the engine intake and exhaust don't net, influence the engine's efficiency. Therefore, it needs through the valve early on or late shut, to make up for insufficient intake and exhaust don't net be short of regret. In this case, will appear a the intake and exhaust at the same time open a moment, with gas phase on call 'valve overlap Angle'. Valve overlap Angle of engine performance often produced great influence, so this Angle much rate should be used? We know, engine speed is high, each cylinder a work cycle to breathe in and exhaust in the absolute time is also more short, so to achieve higher efficiency of the air, they need to extend engine breathe in and exhaust time. Obviously, when the higher the speed, the requirements of the valve overlap greater perspective. But in low speed conditions, too much valve overlap Angle will make waste too much spilled into the inlet end, breathe in quantity may decline, airflow in cylinder will disorder, this time the ECU will also is difficult to air/fuel ratio for accurate control, leading to the idle instability, low speed torque low. If, on the other hand, with gas institutions in low speed conditions only optimized, so the engine can't in high speed higher peak power. So the engine design can choose a compromise plan, can't be in two very different conditions are to achieve optimal state. So in order to solve this problem, requirements with gas phase can according to the engine speed and the different work conditions on the adjustment, high and low speed can be the ideal into, exhaust efficiency, and this is variable valve timing technology development the original intention. Although variable valve timing technology in each manufacturer of the terms is a little different, but the realization way but very much the same. To Toyota's VVT-I technology as an example, the working principle is: the system by ECU coordination control, different parts of the engine ECU real-time sensor to the workings of the report. As in the store has the best ECU valve timing parameters, so the ECU can adjust timing institutions at any moment, which changes the valve opening and closing time, or in advance, or lag behind, or remain the same, this video is below for clear show the working principle of the VVT institutions. Say simply, VVT system is in the camshaft driving end by adding a set of hydraulic institutions, so as to realize the camshaft within a certain range from the point of view of the adjustment, also is equivalent to the valve to the opening and closing time has been adjusted. Most of the valve on market timing system can achieve the intake valve timing in a certain range of stepless adjustable, and part of the engine exhaust the door also equipped with VVT system, and further optimize the combustion efficiency. The traditional VVT technology through the reasonable distribution of the valve open time really can effectively improve the engine's efficiency and fuel economy, but the technology is also have their own limitations and the bottleneck. But on this basis, through the introduction of variable valve lift technology can make up for VVT of regret, thus make the engine more smooth, natural breathing.