VTEC: Honda Engines Redefine the Landscape
February 27, 2009
Honda has always been known for its cutting edge engine technology. The VTEC (Variable Valve Timing and Lift Electronic Control) has proven to be know different and its what has given Honda the edge over its competition once again. Invented in the early 1980’s by research and development engineer Ikuo Kajitani, what we know today as the VTEC grew from the revolution-modulated valve control system first implemented in 1983 in the Honda CBR400. Although other manufacturers have produced their own versions, Honda was the first to pioneer and perfect the technology and then introduce it into wide scale production.
To understand the innovation of the VTEC, one must first appreciate the delicacy of the timing in an engine in relation to the intake and exhaust valves that set in motion by the lobes of the camshaft. Three elements are involved and the shape of the lobes of the camshaft determines each. The first element is timing which refers to the angle of measurement of when the valve is opened or closed in relation to piston position. Lift is the distance the valve lifts off the valve seat. Duration refers to how many degrees of crankshaft revolution the valve is kept open. Because of the differences in behavior in the fuel and air mixture before and after combustion at both high and low rpm, there is also a large difference in the engines performance. The most optimal timing settings at high rpm and the engine will have a lot of power but will give a very rough engine performance at low rpm (where most automobiles spend their time). Set the timing to the low rpm spectrum and the engine purrs like a kitten but has very little engine power. The perfect engine would be capable of having a fully variable timing, adjusting the timing, duration and lift so that the valves would always open at exactly the correct positions no matter what the speed of the engine. The VTEC was designed to marry the ideas of high rpm engine power output and low rpm stability.
In practical application a fully variable valve is difficult to put into application. One way Honda has sought to overcome this is by supplying more than one camshaft shape. So instead of one camshaft lobe setting each valve in motion, Honda has utilized two lobes. One lobe set to provide the low rpm stability and the other set to enhance the high rpm power output. The two lobes are controlled by a computer which constantly monitors engine oil pressure, engine speed and throttle position. The computer then directs which lobe is operating at any given time. The switch over point is variable as well with a minimum and maximum point is ultimately determined by engine load.
The VTEC has high and low lift lobes only on the intake cams however for the next generation; Honda placed variable lobe timing on both the intake and exhaust cams. Honda dubbed the newest innovation the K series.
The DOHC VTEC was originally introduced in the United States in the 1990 Acura NSX. With increased fuel mileage, engine performance and decreased fuel emissions, the VTEC was introduced in several other models including the Acura Integra, Honda Del Sol and the Honda Prelude.
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