How VTEC Works

The Process

1. A standard camshaft is composed of a chain- or gear-driven shaft, with a lobe that depresses the rocker arm as it spins, opening the valves at a set distance. A VTEC camshaft features a set of three lobes with the central lobe extending further out. The longer and shorter lobes of the crankshaft form two different profiles for the electronic control unit to select from.
   
   The rocker arms operate the intake and exhaust valves, opening and closing the valves as the camshaft lobes press against them. A VTEC engine differs from a standard engine through the design of its rocker arms, which uses a set of three arms.
   
   Set between the outer rocker arms is a electronically controlled hydraulic switch that actuates a synchronizing pin to lock or unlock the middle rocker arm. The outer rocker arms have primary control over the valve openings. As the synchronizing pin locks into place, the central rocker arm moves with the extended central lobe, opening the valves farther.
   
   The synchronizing pin consists of two sliding pins separated by a pair of springs. As the hydraulic switch presses the first pin towards the central rocker arm, a spring presses the second pin into place within the third rocker arm. The second spring resets the pins when the hydraulic switch is released.
   
   The electronic control unit, or ECU, monitors the revolution speed of the engine and adjusts between the two camshaft profiles to alter the engine's performance by controlling the hydraulic switch in the rocker arms.

Low RPM

2. At low RPM, the ECU uses the low lift profile, releasing the synchronizing pin to disengage the central rocker arm. This allows the camshaft lobes to actuate only the outer rocker arms, opening the valves less to provide better fuel efficiency and lower power.

High RPM

3. As the engine speeds increase, the ECU engages the switch to lock the central rocker arm into the second high lift profile. As the extended central camshaft lobe depresses the central rocker arm, the valves open farther to allow additional fuel and air into the cylinder. The additional air/fuel mixture inhaled by the motor provides a stronger combustion, which in turn increases power at the expense of higher fuel consumption.

Radityo Wahyu Utomo
XII IA 11/26