VTEC, Variable Valve Timing and Lift Electronic Control is a valve train system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. This system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani. It can be said that VTEC, the original Honda variable valve control system, originated from REV (Revolution-modulated valve control) introduced on the CBR400 in 1983 known as HYPER VT EC. VTEC was the first system of its kind, though other variable valve timing and lift control systems have been produced by other manufacturers (MIVEC from Mitsubishi, VVTL-i from Toyota, VarioCam Plus from Porsche, VVL from Nissan, etc).

i-VTEC

(intelligent-VTEC) introduced continuously variable camshaft phasing on the intake cam of DOHC VTEC engines. The technology first appeared on Honda’s K-series four cylinder engine family in 2001 (2002 in the U.S.). In the United States, Honda first debuted the technology on the 2003 Honda Civic Si EP3 with the economy version.

Valve lift and duration are still limited to distinct low- and high-RPM profiles, but the intake camshaft is now capable of advancing between 25 and 50 degrees (depending upon engine configuration) during operation. Phase changes are implemented by a computer controlled, oil driven adjustable cam gear. Phasing is determined by a combination of engine load and rpm, ranging from fully retarded at idle to somewhat advanced at full throttle and low rpm. The effect is further optimization of torque output, especially at low and midrange RPM.

K-series

The K-Series motors have two different types of i-VTEC systems implemented. The first is for the performance motors like in the RSX Type S or the TSX and the other is for economy motors found in the CR-V or Accord. The performance i-VTEC system is basically the same as the DOHC VTEC system of the B16A’s; both intake and exhaust have 3 cam lobes per cylinder. However the valvetrain has the added benefit of roller rockers and continuously variable intake cam timing. Performance i-VTEC is a combination of conventional DOHC VTEC with VTC.

The economy i-VTEC is more like the SOHC VTEC-E in that the intake cam has only two lobes, one very small and one larger, as well as no VTEC on the exhaust cam. The two types of motor are easily distinguishable by the factory rated power output: the performance motors make around 200 hp (150 kW) or more in stock form and the economy motors do not make much more than 160 hp (120 kW) from the factory.

R-series

The new SOHC i-VTEC implementation is an entirely new implementation that was introduced on the 2006 Honda Civic’s R-series four cylinder SOHC engines. This implementation uses the so-called “fuel economy cam” and “high output cam” on one of the two intake valves of each cylinder (another intake valve is fixed). The “fuel economy cams” are designed to retard the closure of one intake valve and are activated between 1000-3500RPM and under low load condition. When “fuel economy cams” are activated, the intake valve closes well after the piston has started moving upwards in the compression stroke. During this time, the drive-by-wire throttle valve is open wider than normal. Due to the delayed closing of intake valve, a part of the intake mixture that has entered the combustion chamber is forced out again into the intake manifold. That way, the engine “emulates” a lower displacement than its actual one (its operation is also similar to an Atkinson cycle engine, with uneven compression and combustion strokes), which reduces pumping losses thus reducing fuel consumption and increases its efficiency. VTEC-off on the R18A means it can be considered to be running “high output cams”. When the right conditions are achieved for fuel economy, VTEC engages the 2nd set, the ‘low’ or ‘economy’ cams. Thus VTEC-on on the R18A means it is running low cams.

According to Honda, this measure alone can reduce pumping losses by 16%. Under heavier loads, the engine switches back into its “high output cams”, and it operates like a regular 4 stroke Otto cycle engine. This implementation of i-VTEC was initially introduced in the R18A1 engine found under the bonnet of the 8th generation Civic, with a displacement of 1.8 L and an output of 140 PS (100 kW; 140 hp). Recently, another variant was released, the 2.0 L R20A2 with an output of 150 PS (110 kW; 150 hp), which powers the EUDM version of the all-new CRV. SOHC i-VTEC

With the continued introduction of vastly different i-VTEC systems, one may assume that the term is now a catch-all for creative valve control technologies from Honda.

i-VTEC VCM

In 2003, Honda introduced an i-VTEC V6 (an update of the J-series) that includes Honda’s cylinder deactivation technology which closes the valves on one bank of (3) cylinders during light load and low speed (below 80 km/h (50 mph)) operation. The technology was originally introduced to the US on the Honda Odyssey minivan, and can now be found on the Honda Accord Hybrid, the 2006 Honda Pilot, and the 2008 Honda Accord.

i-VTEC VCM was also used in 1.3L 4-cylinder engines used in Honda Civic Hybrid.

i-VTEC i

It is a version of i-VTEC with direct injection.

It was first used in 2003 Honda Stream.

This is how an ivtec engine works

And this is the Honda Hybrid System

Reference: www.wikipedia.org

www.world.honda.com