VTEC stands for Variable Valve Timing and Lift Electronic Control and represents a variable valve control system developed by Japanese car manufacturer Honda for its gasoline engines. The system was the first of its kind and although most car makers worldwide started developing their own variable valve timing and lift control systems, the VTEC witnessed the biggest success becoming a trademark and an integral part of Honda’s consumer perceived identity.History of the VTEC System
Because of the growing demand in the early 80s for high powered sports bike engines Honda embarked on a mission to try and achieve an engine that would display both high power output and driveability over the entire revolution range. So following a feasibility study, Honda’s research and development team set on course to achieve a 200HP per liter power output and stable idling. The team discovered they needed to come up with a method to counteract the air inlet resistance from low to medium engine revolutions.
The solution arrived through the REV (Revolution-modulated valve control) valve pausing mechanism. The system had the task to forcibly stop multiple valves when needed in order to optimize airflow and achieve a stable idling and increased smoothness for low to medium engine operation. The first production motorcycle marketed with the new REV system was the CBR400F in 1983.
From the REV used in motorcycle engines, Honda developed the VTEC valve actuation system for automobiles by building on the idea to have both variable valve opening times and two camshaft profiles: for low to middle engine speeds as well as for middle to high engine speeds. The first Honda automobiles to receive the VTEC system were the 1989 JDM-spec Integra and Civic CRX SiR, which used a 160 hp B16A DOHC engine. The American market received the VTEC system in 1991 with the Acura NSX supersports car which used a DOHC VTEC V6 unit which developed 270 hp at 7100 rpm.
So How Does VTEC Work?
Initially designed for DOHC (Double Overhead Camshaft) gasoline engines, Variable Valve Timing and Lift Electronic Control has the role to switch between fuel saving operating mode to performance operating mode. This is done by running in a low speed valve timing and small cam profile at low engine speeds for improved fuel consumption and leaner fuel burning. On the other hand, when the engine needs more power a higher output is achieved through the VTEC system by speeding up the valve timing and switching to the larger cam profile which allows for a further and longer valve opening time.
The switch from the low profile cams meant for improved fuel consumption to the high profile cams meant for increased power output is done via a locking pin which connects the two independent cam lobes at a certain engine speed. Now depending on the engine’s characteristics this can be set to occur further up the engine range or lower for increased torque but poorer fuel savings. On the returning phase, when the engine switches from high profile cams to the low profile ones, the pin retracts at a lower engine speed than when it first activates in order to avoid the engine running around VTEC activation border.
The VTEC system works much in a way as a mechanical compressor or turbocharger would, by creating a high swirl effect and excellent filling efficiency materializing in higher power output. In terms of reliability, most of you have probably heard in the news regarding the automotive industry that Japan's second largest car maker has an outstanding positive record in this respect and the VTEC units are no exception from this rule.
Honda has developed several VTEC variations over the years, altering the valve system to suit different engine output or fuel consumption requirements. The VTEC system can also be applied to SOHC (Single Overhead Camshaft) engines, but loses the high profile cam advantages on the exhaust side, as there is only one camshaft to activate the lift. So, even with further developments the SOHC engine can benefit from the VTEC system only during either the intake or exhaust side.
To better understand the mechanism we recommend you take a look at the short video clip below, depicting the VTEC activation system.
As mentioned earlier, Honda worked on several variations of the VTEC system:
VTEC-E : is a valvetrain system in which the two normal cam profiles which activate the valves have different sizes. The shorter one allows one valve to open just a small amount and achieve better fuel consumption. As with the original VTEC system, when the engine hits higher rpms, the pin locks the high profile cams and valve timing increases to reach higher power output.
3STAGE VTEC : this variant uses three different cam profiles that literally operate in three stages. Each one controls a different valve timing and lift pattern.
i-VTEC : which stands for Intelligent VTEC is the Japanese manufacturer’s most successful valve actuation system to date and saw broad implementation in production models. The i-VTEC system was introduced in 2001 and uses continuously variable intake valve timing and computer controlled management for optimized torque output and fuel efficiency.
AVTEC : Advanced VTEC was announced by Honda in 2006 and seeks to combine the benefits of the i-VTEC system with continuously variable phase control, which is meant to respond to the driver’s power needs independent of engine speed. Honda announced the AVTEC system will allow for 13 percent better fuel economy over i-VTEC and 75 percent lower emissions than the 2005 standards. As of early 2010, the AVTEC system still hasn’t been implemented in production vehicles.
So what does it do and why is it so important?
Well Honda’s VTEC system represents a very important milestone in gasoline engine research and development because it identified and successfully handled a very delicate matter of any internal combustion engine: operating efficiency. The fact of the matter is most people today, just like most people a century ago, have little knowledge about the working principles of the things that make their daily lives easier and they just take them for granted (like a computer or a car’s engine). So, as you would expect, before this mind-the-environment propaganda began, people settled for thirsty and inefficient petrol engines looking to make their lives better through uncontrolled spending. And why shouldn’t they? After all, progress requires hard work and dedication and who likes that?
Leaving the jokes aside now, what people looked and still look for in vehicles are power and thrilling sound. And as Honda followed for most of its time a policy which believed in passion for engines and doing what you love (an attitude which earned them respect in many countries all over the world and an approach which led to numerous technological achievements most of which never even entered production), they started to work on their engines to better optimize and develop them. Thus, the VTEC valve actuation system was born, which not only increased a gasoline engine’s combustion efficiency, but managed to offer customers the perfect marriage between low fuel consumption and performance characteristics from a single powerplant.
Source;
http://www.autoevolution.com/news/hondas-vtec-system-explained-20338.html