From REV to VTEC. Variable Valve Control System ever evolving
It can be said that VTEC, the original Honda variable valve control system originated from REV, revolution responding type valve pausing mechanism, announced in 1983. Receiving the demand for high power for sports bike engines at that time, prior study was started to reconcile high power in high revolution range and excellent drivability and high efficiency from idling throughout all ranges. An epoch-making variable valve system came into being, which enables to switch over from two valves to four valves. This technology later developed into the variable valve timing mechanism, VTEC (variable valve timing and lift electronic control system), which forms the nucleus of automobile engines.
|REV born from aiming at reconciliation of 200PS per liter and low revolution range performance|
Starting point of VTEC.
Revolution responding type valve pausing mechanism "REV"
|REV is a system to operate four valves in high
speed revolution range in accordance with the revolution of
engines and to reduce the number to two valves in low and medium
speed revolution range. Pause the operation of valves on both
inlet and exhaust sides at the rate of one each per cylinder.
A sensor detects the revolution of engines. Four valve operation
and two valve operation are automatically changed over, performing
the separation and connection of locker-arms by the shift of
hydraulic pistons built inside the locker-arms split into two.
When four valves are in operation, high power is produced in
high speed revolution range while two valves are put into operation,
blow-by of fuel air mixture is reduced, so that flow velocity
is improved. A high swirl effect and excellent filling efficiency
will materialize power improvement in low and medium speed revolution
|VTEC meeting with various requirements, such as practical use types and low fuel consumption types|
|VTEC engines started from the REV for motorcycles have undergone subsequently various evolutions. DOHC VTEC engines with switchover for valve timing and the amount of lift for intake and exhaust system aiming at high power and high torque. VTEC engines with a single cam shaft to drive intake valves, switching over low speed valve timing lift and high speed valve timing lift by attaching importance to the balance in the practical use range. Furthermore, VTEC-E engines, which attempted substantial improvement of fuel consumption by enabling lean burn, suspending one valve in low speed range, in addition to the driving by practical valve timing lift in medium and high-speed range. And, 3 STAGE VTEC engines were put out. Switchover was made literally into three stages, using three cams for low, medium and high-speed operations on air inlet side, suspending one valve at low speed operation and taking switchover motion to valve timing lift in medium speed and high-speed operations.|
|Intelligent new-generation engines, DOHC i-VTEC|
|Honda has further evolved VTEC and newly developed DOHC i-VTEC, reconciling low fuel consumption of world top class and clean exhaust gas and having high power and rich torque characteristics over the entire ranges. For this engine, highly intelligent valve timing lift mechanism, which combines Honda's original VTEC switching over valve timing and the amount of lift in accordance with the revolution ranges of engines with VTC (variable timing control) continually controlling the phase of air inlet valve timing in accordance with the load on engines.|