The valve timing of the engine has an important impact on its power, economy and exhaust pollution. The optimal valve timing should allow the engine to be filled with the most fresh air (combustible mixture) in a short ventilation time, minimize the exhaust resistance, and minimize the amount of exhaust gas residue. When the engine speed changes, because the speed of the airflow and the absolute timing of early opening and late closing of the intake and exhaust valves change, the optimal valve phase angle should also change accordingly. The opening and closing of the engine's valves is driven by the cam, and the early opening and late closing angles of the intake and exhaust valves are fixed. This actually can only make the engine in the best valve phase in a certain speed range, and when the engine speed is When it is very low or very high, its gas matching phase will be in an unsatisfactory state.
At low engine speeds, because the valve stacking angle is larger than the ideal value, part of the fresh mixture is taken away by the exhaust gas, resulting in increased fuel consumption and emissions; at high speeds, due to the valve stacking angle Less than the ideal value, the air intake volume is insufficient, thus limiting the maximum power that the engine can achieve. In order to improve engine performance, variable valve timing and valve stroke technology have become an important research topic in the field of automotive engine technology. So far, a variety of engine valves with variable valve phases have appeared, which have improved the power, economy and exhaust pollution of these engines.
Foreign research institutions have long conducted a large amount of research on variable valve timing. Patents related to variable valves have appeared in the United States since 1880. By 1987, there were nearly 800 patents. In recent years, Still developing continuously. . However, many mechanisms that appeared before the 1980s have many problems, such as high cost, complex mechanisms, limited adjustable degrees of freedom, and high impact loads. In the past 20 years, the development of electronic technology has promoted the commercialization of variable valve phase mechanisms. Some technologies have been successfully used in automobiles and achieved good results.
Honda launched its self-developed "Variable Valve Timing and Valve Lift Electronic Control System" in 1989. VTEC is the world's first valve that can control valve opening and closing time and lift at the same time. control system. Honda's VTEC engine has always been known as "synonymous with variable valve engines". It not only outputs super power, but also has the characteristics of environmentally friendly exhaust emissions at low speeds and low fuel consumption. Such completely different characteristics are in the same engine. It appears because it has a variety of cams with different angles on one camshaft.